Tylopterus boylei is known in only a single specimen preserved as a mold of the dorsal surface. Guttapercha squeezes of this show that the knots are not located on the first to fourth segments as stated in the original description but on the second to fifth. The squeezes also show distinctly the ocelli on the prominence between the lateral eyes. On the right side also two segments of the fourth ectognathite (balancing leg) are seen and on the opposite side the edges of two flat segments, apparently the oar plate of the swimming leg. The legs seem, therefore, to have agreed with those of Eurypterus.
Subgenus ANTHRACONECTES Meek & Worthen[1]
Meek and Worthen suspected that their species Eurypterus mazonensis from the Lower Coal Measures (Pennsylvanian) represented a distinct subgenus, if not a genus, for which they proposed the name Anthraconectes. They state that this fossil "differs from the typical forms of Eurypterus particularly in the great length and single extremity of the mesial appendage of its operculum, as well as in the possession of two little spatulate supplementary pieces." Hence they "strongly suspect that other characters will be found, when better specimens can be studied, showing it to belong to a distinct subgenus, if not indeed to an entirely distinct genus from Eurypterus proper."
Hall suggested that these differences may not be of great importance [op. cit. p. 26] and emphasized the fact that the species from the Pennsylvania Carbonic are typical Eurypteri [p. 27].
While we agree with Meek and Worthen that the peculiar character, of the opercular appendage would warrant a separation of the species from typical Eurypterus, we believe that the preservation of this organ is not so distinct that its characters are beyond doubt. On the other hand, we have no doubt that Anthraconectes mazonensis has a number of characters in common with the Pennsylvania and also with British Carbonic species which distinctly indicate a phylogerontic condition
