CRUSTACEA. 129 



Proetos Nevad/E, n. sp. 



PLATE XXIII, FIG. 19 

 ProStus marginalis, Walcott. MonogT. V. S. CJeol. Surv., vol. viii : Pal. Eureka Dist.. ]>. 210. 1884 



The specimen identified by Mr. Walcott as Proitus marginalis, Conrad, in the 

 work above cited, is a well-preserved and nearly entire individual, which ex- 

 hibits points both of relationship and difference with the various representatives 

 of the group of Proifus typified by P. Rowi, viz. : P. angustifrons, clarus, mar- 

 ginalis (= Rowi) and Prouti. All these species are established upon differences 

 which are of themselves slight but which nevertheless appear persistent. To 

 any of these species, as here described, it becomes impossible to admit the 

 Nevada form, as it differs from each member of this group in as many 

 respects as those species differ from one another. It therefore seems neces- 

 sary to regard it as having a distinct specific value founded upon characters 

 which may be best expressed by a comparison with each of the species above 

 mentioned. 



With P. angustifrons it agrees (a) in the character of the frontal border, which 

 is convex near the marginal sulcus and slopes evenly to the edge, becoming 

 faintly concave on the anterior limb ; (b) in the relatively narrow glabella, tan- 

 gential upon the frontal border (in the type specimen the glabella has been 

 slightly compressed laterally and thus appears somewhat narrower and more 

 convex than is normal) ; (c) in the number of annulations upon the pygidium. 

 It differs from this species in (a) the narrower and more elongate body; (b) the 

 much smaller eyes ; (c) the broader, more elevated and convex cheeks ; (d) the 

 longer and more slender genal spines ; (e) the narrower and more elevated 

 pygidial axis. 



With P. clarus it agrees in (a) the character of the frontal margin ; ()>) the 

 length of the genal spines; (c) the form, contour and annulations of the pygi- 

 dium. It differs from this species in (a) the much narrower and more regularly 

 elliptical body ; (b) the much narrower glabella ; (c) the smaller eyes ; (d) the 

 narrower, more arched and more slowly tapering thoracic axis; (e) the narrower 

 pygidial axis. 



