Page:The Eurypterida of New York Volume 1.pdf/132

 retained its primitive character; and while the legs are of uniform length in Pterygotus, in all other eurypterids, mature and adolescent [, pl. 2], they form a series that is longer backward. It is therefore to be concluded that, even if the legs were originally of uniform length, a differentiation in length took place very early. The relatively great length of the few segments observed in Strabops indicates that the last pair of legs had attained considerable length and that the differentiation had already commenced in the Cambric. We have accordingly restored Strabops with a series of gradually lengthening slender, nearly spineless legs and would provide the prototype with a similar only more uniformly long series of legs.

The chelicerae, or preoral appendages, are of identical structure in all—only excessively enlarged in Pterygotus—and therefore not available for inferences as to the prototype except that it had them as seen in the majority of the forms.

The opercular appendages have not been observed in either the larvae or in Strabops and are therefore useless for the present inquiry. Laurie has suggested that the median lobe of the genital operculum in Pterygotus shows a less degree of development than in Slimonia and Eurypterus, but