80 PROCEEDINGS OP THE ACADEMY OF 



sion, ornamented with a few very small pustules, upon which small secondary 

 spines probably articulated. Primary spines, apparently one inch or more in 

 length, rounded, slender and nearly or quite straight, with the articulating 

 end perforated and a little enlarged, so as to form an undefined ring: surface 

 ornamented with minute, crowded, longitudinal striae, only visible by the aid 

 of a good magnifier. 



Ambulacra narrow, or only about equaling the breadth of the marginal 

 rows of interambulacral plates on eacli side, slightlj"- convex. Ambulacral 

 pieces slightly imbricating in the opposite direction from the interambulacral 

 series, of very unequal size and form, and irregularly arranged, most of those 

 starting from the mesial zigzag suture, extending out so as to connect with 

 the crenated lapping margins of the outer ranges of interambulacral plates, 

 while many of those starting from the latter inward, wedge out more or less 

 abruptly between the others, at various distances before reaching the mesial 

 suture, so as to present the appearance of a strong tendency to run into two 

 rows of pieces on each side of the mesial suture; each pierced by two pores, 

 which, owing to the irregular arrangement of the plates, present the appear- 

 ance of forming two double rows along near each lateral margin of each 

 ambulacrum, or four rows to each of these areas. They might, however, with 

 probably almost as much propriety, be counted as one double, strongly zigzag 

 row on each side. 



Near what appears to be the position of the oral opening, there is adhering 

 to the specimen one half of a stout jaw, 0-60 inch in length. On its outer side 

 it is cuneiform, a little arched, and provided with a broad, longitudinal, ex- 

 centric furrow ; its lateral margins are smooth, and near 0-30 inch in breadth 

 at the base, and converge to a sharp edge within. We have now tolerable 

 good evidence that all the different genera of the Perischoechinidx are pro- 

 vided with strong jaws. 



The specimen is too imperfect to give a good idea of its general form or size. 

 As it shows one of the interambulacral areas, however, to be near two inches 

 broad, it is probable the entire fossil was not less than four and a'half inches in 

 its transverse diameter. The largest interambulacral plates measure 'about 0-35 

 inch in length and breadth, while those of the outer rows next the ambulacra 

 are proportionally narrower. The primary spines seem to be about one inch 

 or more in length, though we have seen none entire. The longest fragments 

 we have seen, are about half an inch long, 0-10 inch in thickness at the 

 articulating end, and 0-06 inch in diameter a little above, but without any 

 taper toward the broken end. The ambulacral areas are only about 0-20 inch 

 in breadth at the widest place, near the middle, and about four to six of their 

 pieces fit into the crenulations of each of the marginal interambulacral plates. 

 We have been somewhat puzzled in regard to the generic characters of this 

 species. Its interambulacral plates are each provided with the large central 

 tubercle and spine, characterizing Archeeocidaris and Eocidaris, though these 

 tubercles agree with those of Eocidaris in having no ring or slight projection 

 around the base, as in Archeeocidaris. At first we were inclined to believe it 

 related to Prof. Hall's genus Lepidechinus, on account of the decidedly imbri- 

 cating character of its plates ; but judging from the brief published descrip- 

 tion of the type of that group (which has not yet been figured), it would seem 

 to belong even to a different family, or sub-family, as nothing is said in the 

 description of that type in regard to a large central tubercle for the articula- 

 tion of a larger spine, on each of the interambulacral plates, the surface being, 

 on the contrary, merely described as crowded with "irregular granules." In 

 addition to this Prof. Hall places his group as a sub-genus under I'alivchinus, 

 one of the distinguishing features of which is the presence of numerous small 

 imperforate tubercles covering all the plates, without any larger central perfo- 

 rated tubercle. 



It is worthy of note, however, that Prof. Hall has since figured and described 

 another species [L. rarispinus, Twentieth Rep. Regents Univ. N. Y. on State 



[April, 



