THE EURYPTERIDA OF NEW YORK
27
attachment scars as the eurypterids. Even in the mature Limulus, the extensors, or abductors, and the flexors, or adductors, of the gillbearing ventral plates are still subdivided into many radiating fasciculi, and likewise the extensors and flexors of the tail spine arise from a large number of fasciculi.[1]
The longitudinal zones or series of scales are especially distinct in Eurypterus remipes [pl. 8, fig. 5] and lacustris. They inclose here a distinct smooth, flat median zone, which corresponds to the course of the intestine and there is reason to believe that this double series of scales marks the bases of the muscles and suspensory organs of the intestine. In Pterygotus the distal portion of the intestine
- ↑ The muscles of the eurypterid cephalothorax were probably contracted into solid bundles, as in Limulus, following the solidification of the segments. This is indicated by the occurrence of a pair of entapophyses, or chitinous infoldings of the carapace [pl. 6, fig. 6],
Figure 4 Dorso-ventral muscles on carapace of Eurypterus
le, lateral eyes; ce, ocelli; 62, median dorsopreoral-entosclerite muscle; 63, anterior dorso-plastron muscles; 64, median dorso-plastron muscle. (From Gaskell) corresponding in their position to those observed in Limulus, and also by the observation of pairs of circular or oval areas arranged along the median line. At least three such pairs of areas have been seen in Eurypterus remipes. The foremost of them is shown in plate 5, figure 7. They may correspond to the first pair of tergo-proplastrals in Limulus which suspend the anterior horns of the entosternon from the dorsal side of the carapace. Gaskell has drawn a hypothetical restoration of the muscle system of the cephalothorax of an Eurypterus [text fig. 4] by inserting in the carapace of E. scouleri the segmental dorso-ventral muscles as met with in the living scorpion. In a general way this is corroborated by our observations, with the exception that the muscles do not appear to be arranged so closely around the center of the carapace, at least in Eurypterus remipes. From evidence presented subsequently it would seem preferable to use Limulus as the basis of such restoration.
