Page:The Eurypterida of New York Volume 1.pdf/127

 of the abdomen and the smaller size of the telson. In these palingenetic characters the nepionic stage resembles so much the Cambric Strabops, that we shall designate this as the Strabops stage. We shall use these characters in the reconstruction of the primitive ancestor of the eurypterids in the next chapter and the discussion of their taxonomic position.

In reference to this taxonomic position it may be stated here that the ontogeny of the eurypterids fully corresponds to that of Limulus in lacking any indication of a nauplius or zoea stage; that the larvae of the eurypterids (nepionic stage) have in common with that of Limulus:


 * 1) The large size of the carapace
 * 2) The broad border of the latter (in  )
 * 3) The prominent cardiac region of the carapace, giving it a trilobate character (in ,  ,  )
 * 4) The lack of differentiation of the abdominal segments
 * 5) The undeveloped telson.

They differ from it in:


 * 1) The terete abdomen
 * 2) Megaloptic development of the lateral eyes, and
 * 3) Their nearer approach to the margin
 * 4) Having but nine abdominal segments, while Limulus is hatched with the full number of segments.

The meaning of these agreements and differences in the development of the eurypterids is discussed more advantageously in the chapter on the taxonomic relations of the eurypterids where also the ontogeny of the eurypterids is compared with that of the scorpion.