PALEONTOLOGY. 455 



them as a natural group, sufficiently marked to be readily distinguished. 

 I therefore propose to recognize them as a distinct genus under the gen- 

 eric name Echinocaris, possessing the following characters : 



Genus ECHINOCARIS Whitf. 

 Echinocaris Whitfield, 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 mpre or less 

 distinctly elevated, curved, longitudinal ridge, centrally or subcentrally 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, composed of several segments (four 

 known) and a caudal plate, which is produced into an elongated spine with a lat- 

 eral, movable spine on each side. Posterior margin of the abdominal segments 

 bearing spines on the now known species. 



Type Echinocaris sublevis Whitf. 



Among the genera now known and referred to of the Ceratiocaridtz 

 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 fol- 

 lowing synopsis of some of their characters may serve to illustrate their 

 peculiarities and to show more distinctly the relations which Echino- 

 caris bears to other known genera : 



1st Section : Carapace more or less elongated, with a straight or slightly arched 

 dorsal line; anterior end sharply rounded or pointed (rostrate); posterior end 

 truncate ; sides convex, smooth or simply striate, sometimes marked by a simple 

 ocular node near the antero-dorsal margin;, no r'dges or other nodes. Ceratiocaris 

 McCoy, 1849; Caryocaris Salter, 1862; Hymenocaris Salter, 1852; Solenocaris 

 Meek, 1872; (?) Colpocaris Meek, 1872. The last somewhat questionable in char, 

 acter. 



2d Section: Carapace similar in form to that of Sect. 1, with the postero- 

 basal angles produced into spines, and the surface with longitudinal ridges- 

 Diihyrocaris Scouler (= Argas Scouler). . 



3d Section: Carapace rounded at both extremities, elongate-elliptical or 

 elongate-ovate in form with a straight dorsal margin ;_ surface concentrically 

 striate, no nodes or ridges. LmguLocaris Salter, 1866. 



4th Section : Carapace triangular, dorsal margin straight ; surface punctate or " 

 reticulate, and concentrically striated (growth lines ?). Dictyocaris Salter, 1860. 



5th Section: Carapace suboval or subovate with a straight hinge-line; sur- 

 face marked with longitudinal ridges or representative nodes and ridges. Surface . * 

 of parts smooth, punctate or pustulose. . Echinocaris new gen. 



6th Section : Carapace broadly oval or ovate, no straight cardinal line, con- 

 sequently no hinge, anterior end rostrated or beaked, surface destitute of nodes or 

 ridges. Physocaris Salter, 1860. 



7th Section : Carapace composed of three pieces, or apparently of three ; two 

 of which are semi-circular, with the anterior end of each obliquely truncate, form- 

 ing when the two are united, an anterior triangular notch into which the third or 

 rostral plate is inserted. Surface concentrically marked by growth lines ; no nodes 

 or ridges. Peltocaris Salter, 1866 ; Discinocaris Woodward, 1866; Aptichopsis Bar- 

 rande, 1872; Pterocaris Barrande, 1872 (not Heller, 1862). 



