114 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



outline slightly angulated medially, the outer part of the flat border 

 with a delicately tri-striated band forming a barely raised rim ; dorsal 

 furrows moderately impressed between the posterior edge and the 

 eyes, obsolete forward; neck furrow unrecognizable exteriorly, but 

 a very narrow neck ring is suggested on interior casts ; palpebral 

 lobes of medium size, drooping but sHghtly, situated entirely beliind 

 the midlength ; posterior limbs short and not much attenuated laterally. 



"■ Free cheeks, . subtriangular, depressed convex, without elevated 

 border ; but having a long genal spine which is directed more outward 

 than backward. The anterior edge of the cheek is bent near its middle 

 and nearly straight on either side, the outer of the straight halves 

 extending to the tip of the genal spine, the other to the facial suture. 

 Here the edge passes to the doublure, the direction at the same time 

 having to bend a little forward so as to conform with the obtusely 

 angular frontal edge of the cranidium. 



" Thoracic segments narrow, nearly smooth or at least not deeply 

 furrowed, the axial and pleural parts approximately equal in width, 

 the extremities tapering almost to a point without recurving. 



" Pygidium, exclusive of spine, broadly triangular, fully twice as 

 wide as long, unsegmented exteriorly ; axis convex though obscurely 

 defined exteriorly, fairly well defined and with traces of three or 

 four segments in casts of the interior, extending to the posterior edge 

 beyond which it is prolonged as a slender and relatively long spine ; 

 pleural lobes gently convex, divided obliquely into subequal parts by 

 an obscure linear depression or groove, otherwise smooth." 



Observations. — " Intimately associated with the typical form of the 

 species are two other kinds of cranidia, but only one other kind of 

 pygidium has been observed with them. Though distinguishable, 

 this pygidium and at least two of the cranidia seem too closely allied 

 to warrant specific discrimination with the material in hand. Pro- 

 visionally, then, I propose to distinguish them as varieties. The third 

 is so much shorter and more convex than the others as to suggest a 

 distinct, though doubtless allied, species. However, as only a single 

 example has been observed, it seems advisable to recognize it pro- 

 visionally as another variety. 



" The rock in which the type specimens occur is a light-gray, 

 laminose limestone, filled with fossils. The same layer contains 

 Apatokephalus UnaVis (Walcott)." 



Formation and locality. — Ozarkian : (201a) Goodwin formation. 

 East slope of the ridge east of Hamburg Ridge. Eureka Di.strict, 

 Eureka County, Nevada. 



