732 



Report of the State Geologist. 



of the valve. The anterior convexity is much the larger. Usually, in Echi- 

 nocaris, there is a number of paired nodes and tubercles grouped about the 

 cephalic extremity of the carapace, but in this fossil there is only a single 

 pair, represented by two deep pits situated close upon the hinge and at the 

 apex of the rostral cleft. It is possible that these are remains of ocular 

 nodes, but their depth suggests the probability of their having been basal 

 attachments of the larger legs. Behind these nodes begins an oblique and 

 strong ridge, thickest and most elevated at the hinge, where the anterior 

 edges of the ridges on the two valves meet. This ridge departs backward 

 into the median groove, passes down its anterior slope, then, with a slight 

 change of angle, along the groove and rises slightly on its opposite slope, 

 terminating with the groove itself. The margin of the carapace is some- 

 what thickened and elevated. 



Nowhere in Echinocaris do we find a carapace structure like this, even 

 among the species of the Chemung group. The lateral curved carina is one 

 of the constant characters of the genus and may even be duplicate in later 

 species. The median sinus exists there, normally, only as a depression 

 between nodes, and no species is so free of cephalic nodes as this. 



As to the abdominal segments, we find that three, and a portion of a 

 fourth, protrude beyond the carapace ; between the carapace-valves we make 

 out traces of two or three others, estimating the entire 

 number at seven. The posterior segments are unusually 

 short and have short spinules at their post-lateral extremi- 

 ties ; there may, also, have been such spinules elsewhere along 

 the posterior edge as in Echinocaris, but such are not seen. 

 The caudal plate is short and triangular, with a short telson 



and two long curved cercopods. 

 Figure 2. 



Pephricams horri- -"- ne fossil bears a striking ornamentation or armature. 



piiata, margin of en ^ re outer margins of the carapace valves carry a 



left valve. & 1 \ 



single row of broad, strong, erect and slightly recurving 

 sj tines. These are shortest at their commencement on the anterior margin, 

 gradually increase in size posteriorly, their greatest length being reached 

 on the post-lateral curve, and thence to the posterior angle of the 

 carapace they become shorter. The maximum length attained by these 

 spines is not less than one-half of the greatest diameter of a carapace valve. 

 That these processes are spinous extensions of the chitinous test substance, 

 and not bundles of seta-, or of other nature, is shown by the aspect of the 

 imprints they have Left in the matrix, these being sharply defined 



