6 SVEN LOVEN, ON A RECENT FORM OF TIIE ECHINOCONID.^3. 



the trivium. Of the posterior interradium, 5, much is gone, 

 but it presents a deep and broad emargination, the margin 

 of which has all the appearance of being the unhurt hinder 

 portion of the periproct, the large opening of which in the 

 living animal was covered över with the anal membrane. 



The features thus detailed: the central stoma provided 

 with internal auricles for snpporting a dental apparatus; the 

 excentric posterior periproct; the simple and straight zones of 

 pores; the perforate and crenulate tubercles, all point towards 

 that oldest group of neonomous Echinoidea, the Echinoconidse, 

 and among these, bv more than one trait, towards the o-enus 

 Py gäster Agassiz. 



The ambitus is sub-pentagonal, not distinctly so, as in 

 most of the larger Pygasters, for instance the P. Morrisi 

 Wright ^), the punctuated oiitlines of which surround the ji(/^ 

 1 and 2, but plainly enough to be observed at the first giance, 

 and not much less so than in certain middle-sized or smaller 

 species, as the P. Gresslyi Desor or P. laganoides Agassiz -). 

 Owing to the loss of a part of the calycinal region the rela- 

 tion of the central heio-ht of the test to its leno-th is not to- 

 be made out exactly, but may be assumed to have been at 

 least as 0,6 2. This is a greater proportion than that gene- 

 rally observed in Pygasters, in which the mean relation of the 

 height to the length seems not much to excede 0,5. The 

 dorsal convexity is in no wise sub-conical, but presents a con- 

 spicuous gibbousness in its anterior portion, thus reminding 

 of the Py gäster umbrella Ag.^) and P. Gresslyi Des., and 

 of the genera Galeropygus and Hyboclypeus among the Echi- 

 noneidae. The flanks are more regularly rounded, and the 

 ventral surface is not approaching to flatness as in most Py- 

 gasters, biit sub-pulvinate as in the P. Gresslyi. 



The external aspect of the stoma and the peristomal re- 

 gion, Pl. 1, pg. 4, ö, 7, is not a little diflerent from that of 

 the same parts in species of Pygaster, at least as far as I can 

 judge from the specimens at hand of the P. semisulcatus Phil- 

 lips, Pl. 2, fig. 11. In this species the first three ambulacral 

 plates of each series are strongly depressed and united so as- 



') Brit. Ool. Echinod., t. XX, f. 1. 



^) COTTEAU, Pal. Franc, Jura, p. 485, pl. 131—13.3; p. 4G7, pl. 122, 

 f. 1—5. 



^) Ibidera p. 474, pl. 125. 



