s A HISTORY OF CORNWALL crustaceans, he ' went over nearly the same ground as Mr. [Vaughan] Thompson and others, and would have done the same by M. Rathke, but could not, from the river crayfish not being found in our streams.' l Mr. Geo. Penrose, writing from the Royal Institution of Cornwall, Truro, 8 June, 1 903, says : ' I have been making inquiries about the occurrence of the crayfish in Cornish streams, but have not been able to get any record of it.' Rathke was at first reluctant to believe in the metamorphoses of crustaceans, because he had found the young crayfish to be at birth very like its parents. But on further research he very candidly acknowledged that the case was exceptional. The tribe Penaeidea owes its inclusion in the Cornish fauna solely to the industry of Mr. Cocks, who reports ' Penaeus trisulcatus, Leach. from stomach of Morrhua vulgaris, and Morrhua aeglefinus ; rare.' This record appears to have been overlooked by all our later authorities. The Mediterranean prawn intended, is more commonly known by the name P. caramote (Risso), now identified with the much earlier P. kerathurus (Forskal). In this genus the first three pairs of legs are all chelipeds, but the first pair is the shortest and the third the longest, and they carry exopods or outer branches after the manner of the Schizopoda which will be subsequently mentioned. The Caridea, a tribe including most of the crustaceans commonly known as shrimps and prawns, are exemplified here not only by many of the common species in great abundance, but by several of those that are rare in English waters. For the family Crangonidae it will be convenient to quote the statement by Cocks, who groups together several species under the genus Crangon (Fabricius) : ' Crangon vulgaris, Fabr. In pools and sandy shores ; very common. fasciatus, Risso. From the stomach of Trigla hirundo ; rare. spinosus, Leach. In the stomach of the Trigla hirundo, Trigla lyra, G. luscus : trawl refuse ; not uncommon. sculptus, Bell. In the stomach of the Trigla hirundo ; rare. trispinosus, Hailstone. Several mutilated specimens from the stomach of the Trigla lyra ; rare. bispinosus, Westwood. Trawl refuse, stomach of the Trigla lyra ; rare. Dr. Vigurs procured a specimen under a stone, Bar Point.' In this family the first legs are subchelate, the fixed finger being too short to form a proper chela ; the last three pairs of legs are simple. In the members of the family present here the second legs are minutely chelate. Couch speaks of Crangon vulgaris as the ' Sand Shrimp,' and calls Leach's Pontophilus ipinosus the ' Rough sand shrimp.' He follows Milne-Edwards and is followed by Bate in assigning the latter to the genus Crangon, and in supposing it to be the same as Aegean cataphractus (Olivi). Couch says : ' I have possessed only one specimen, which came from the stomach of a fish taken at a depth of from 1 2 to 15 fathoms.' a Bate says : ' We have taken it frequently among the zoophites [zoophytes] from six to sixteen fathoms of water.' 3 Pontophilus, having seven pairs of branchiae, differs thereby from Crangon which has only five, and from Aegean which has eight, and P. spinosus further differs from Aegean cataphractus by having only five rows of teeth on the carapace in- stead of seven. Leach, after describing the former species, says : ' This curious animal was discovered by C. Prideaux, Esq., amongst some rubbish dredged in the Sound of Plymouth, near the Edistone ; a second specimen was afterwards taken off Falmouth, by the late Mr. John Cranch, zoologist to the Congo Expedition.' 4 Which of the two rather easily confused species may have been taken by the other authorities it is perhaps no longer possible to determine. Under the heading ' Crangon boreas Arctic shrimp. Phipps', Bate says : ' There can be little doubt but that C. fasciatus and C. sculptus are identical with C. boreas of Phipps. I have compared the animals with the description and figures of the respective authors, and feel sure that the variations between the several forms are de- pendent upon habitat, those of the Arctic and more northern forms having the spines more strongly developed. Found occasionally on stony ground in about 20 fathoms of water.' 6 Later authorities by no means share Bate's view that these three species are identical. The Arctic shrimp has actually been removed to a separate genus, and the other two are distinguished by Carus under Aegean* Westwood's Crangon bispinosus (1835) has been placed successively under the generic names Pontophilus, Cheraphilus, Philocheras. It takes precedence of Kroyer's dwarf shrimp, Crangon nanus (1842), with which it has been identified, and should now therefore be known as Philocheras bispinosus (Westwood). 7 As to Crangon trispinosus, Bate says : ' Strictly this is not Cornish,' he himself having only taken it in the neighbouring county. But he overlooks the record from Falmouth. Lastly, the reader may be reminded that the distinguishing dark band across the fourth pleon segment of Aegean fasciatus is found also on Philocheras neglectus (Sars). No one apparently except Jonathan Couch has observed Autonomaea olivii, Risso, on the English coast. By Risso the genus is distinguished from Processa by having both limbs chelate in the first pair and from Alpheus by having the second pair simple instead of chelate. The second an- tennae are much longer than the body, and Couch no doubt is referring to this feature in calling it 1 Cormo. Soc. (1843), p. 30. ' Fauna, p. 79.
- ' Revision,' p. 35. 4 Mai. Pod. Brit. July ist, 1817, text to PI. XXXVII".
5 ' Revision,' p. 35. 6 Pndr. Faun. Medit. (1885), p. 483. 7 See South African Crustaceans (1900), pt. I, p. 48, where I have wrongly adopted KrOyer's specific name 270
