Contributions to Invertebrate Palseontology. 563 



of parts of individuals of distantly related generic forms, to be in- 

 closed in the same small concretion ; so we may safely conclude, 

 that, where parts or fragments of individuals of corresponding size 

 are found in the same concretion, they are parts of one individual, 

 or at most, of the same species. In the concretions in question, 

 there are tM^o examples Avhere parts of the naked abdomen and 

 caudal plate with its accompanying spines, are imbedded in the 

 concretion together with the carapace which I have classed as of 

 the same species. This I consider as ample proof that the parts 

 belong to the one individual ; and that the animal of which they 

 are the remains, was provided with a naked body and spinose 

 caudal appendage as in Ceratiocaris. It is also stated in the Illust. 

 Dev. Foss., that one specimen resembling C. punctata, has been 

 found with a body similar to that called C. armata, attached to 

 the carapace, showing their individual relations. 



The several species above mentioned, while differing greatly from 

 Ceratiocaris, possess features in common which at once character- 

 ize them as a natural group, sufficiently marked to be readily dis- 

 tinguished. I therefore propose to recognize them as a distinct 

 genus under the generic name Echinocaris possessing the following 

 characters : — 



Genus ECHIIVOCARIS Whitf. 



Echinocaris Wliltfield, Am. Jour. Sci. and Arts, 3d series, vol. 19, p. 34, 1880. 



Carapace bivalve, valves subovate in outline ; united on the dorsal margin 

 by a straight hinge ; the anterior, basal, and posterior margins rounded, and 

 generally more or less produced posteriorly. Surface of the valves marked 

 by a more or less distinctly elevated, curved, longitudinal ridge, centrally or 

 subcenlrally situated ; also by one or more (usually three) vertical ridges, or 

 ridge-like nodes, extending from the hinge-line on the body of the valve, and 

 usually situated anterior to the middle of the length. Abdomen naked, com- 

 posed of several segments (four known) and a caudal plate, whicli is produced 

 into an elongated spine with a lateral, movable si)ine on each side. Posterior 

 margin of the abdominal segments bearing spines on the now known species. 



Type EcJiinocaris sublevis Whitf. 



Among the genera now known and referred to of the Ceratio- 

 caridse there are several distinct types of structure, indicated by 

 the features of the carapace alone, independent of the changes which 

 take place in the abdominal segments and in the caudal spine and 

 appendages. The following synopsis of some of their characters may 

 serve to illustrate their peculiarities and to show more distinctly the 

 relations which Echinocaris bears to other known genera : — 



