58 S. LOVEX, ON POURTALESIA, A GENUS OF ECHINOIDEA. 



besjins with the homoiopodous Echinoneus ^), jig. 132, which, as in other parts besides, 

 retains an Archa^ononious character in the structure of its disciferous pedicels and 

 their peripodia, very like those of an Echinus, geminous, with the pores nearly equal. 

 In the Cassidulida?, Jig. 133, the new order has set in, the peripodia of the five petala 

 being branchial, and very different from those of the phyllodes. In Cassidulus these 

 last are deep, oval depressions, with the bottom sloping toAvards the adoral end, near 

 which is the single perforation. In the Spatangida;, including the Collyrites and Anan- 

 cites, the phyllodean peripodia, by their superior size, gradually become more and 

 more prominent, at the same time assuming a character of their own that corresponds 

 to that of their pedicels specialised into organs of sense. They are shown in jig, 134 

 — 148^1 all IV a 1, ear-shaped expansions, contrasting with the rest of the surface by 

 a compact and glossy texture, generally of an obovate outline, the longitudinal axis 

 pointing adorally, and mostly towards the mesial suture of the ambulacrum. Within 

 this expansion, the boundary line of which is slightly impressed, while its surface is 

 in some forms convex, in others flat or even depressed, the perforations, as long as 

 geminous, are placed on the longitudinal diameter, the adoral perforation, which is 

 always present, mostly being the larger of the two, while the aboral has a tendency 

 to abort. Thus it seems to be the rule, that in the early types, the Adete, Meri- 

 dosternal ^) forms, both perforations are maintained. In Holaster scaniensis Cotteau, 

 jig. 134, they are separated by the highest part of the convex surface, and in Anancites 

 ovata, jig. 135, minute, and kept apart by an ovoid protuberance, — and so it is 

 in both the two peripodia of IV a 1. The distal peripodium of Hemipneustes, jig. 

 136, shows only a trace of the aboral perforation, while in the proximal it has dis- 

 appeared. In Echinopatagus, jig. 137, one of the earliest of Amphisternal ^) forms, the 

 perforations of IV a 1, reduced in size, are geminous, the bridge being almost as 

 in the Echini. Among the Prymnadetes the two perforations are maintained in 

 Hemiaster, jig. 138, and in Faorina, jig. 142, in others the aboral perforation aborts. 

 How this is done may be observed in Schizaster japonicus, jig. 140, or in Sch. Mose- 

 leyi. The aboral perforation contracts, and is moved towards the adoral, while the 

 bridge gradually narrows, till at last it opens, and the two make one, the trace of the 

 passage being overgrown with calcareous tissue. In fullgrown specimens of Schizaster fra- 

 gilis there are still some geminous perforations left, in Sch. gibberulus and in Moira 

 atropos they are all simple. So they are also in adult specimens of Agassizia and 

 Desoria, while in Abatus Philippii a process obtains similar to that in Schizaster ja- 

 ponicus. Lastly, among the Prymnodesmians, the latest and the most advanced of 

 Neonomous Echinoids, the geminous pore, strictly kept up even as far as from Melo- 

 nites, and discarded in a few only of the Prj^ranadetes, their elders, is replaced, as it 

 seems universally and normally, by a single perforation. So it is in Micraster, Bris- 

 sopsis, jig. 143, Brissus jig. 144, Spatangus jig. 145, Lovenia fig. 146, Maretia fig. 147, 

 Echinocardium, fig. 148, and in Meoma, Plagionotus, Breynia, Eupatagus. It is a 

 change that implies a certain amount of modification in the vascular apparatus. — 



') Etudes, pi. IX. -) BIsQig, piece. ^) ^ficpigisQrog, with two breast plates. 



