82 S. LOVEN, ON POURTALESIA, A GENUS OF ECIUNOIDEA. 



V. THE POURTALESIAD^. 



Tlie characteristics of tlicir skeleton. Tliey constitute a distinct family equivalent to that of the Spa- 

 tani^idnf! and tlie Cassidnlida-. Their geoa:raphical and batlivmetrieal <listribiition. 



Eiijht, species comprised in the genus Pourtalesia, one Echinoci'cpis and one 

 8|)atagocystis, make the whole of what is known at present of the little grouj) discuss- 

 ed in the foregoing pages with regard to its skeletal morphology. It remains to 

 expose its characteristics in a comprehensive form, and to determine its systematic 

 position. In this attempt I feel all the inconvenience of being able to speak, from 

 immediate observation, of but a single species in an entire condition, of three others 

 in a fragmentary state only, and of having had before me no specimen at all of S])atago- 

 cystis. It so happens, moreover, that Pourtalesia Jeffreysi, the only species examined 

 with some degree of completeness, appears to be, in certain respects, of a more advan- 

 ced character than the rest, and therefore, as being less in harmony with their mode 

 of conformation, perhaps not rightly to be regarded as embodying the typical features 

 of the group. However, notwitlistanding these shortcomings, and with the reservation 

 therein implied, and calling to mind that this is not the first occasion, nor will be 

 the last, when a species tliat chances to be the most familiar to us, is put forward 

 as the type of its kind, I venture on the f(dlowing description, with Pourtalesia Jeff- 

 reysi in the foreground. 



The general form of the skeleton of the Pourtalesiadas is more lengthened than 

 that of most other Neonomous Echinoids, sub-cylindroid or ob-conical; anteriorly more 

 or less truncate, sometimes ])road; in the middle slightly tumid; posteriorly tapering; 

 (lorsally convex, sometimes even raised into a liuinp; ventrally rather flat. Below 

 the slightly overhanging front the forepart is invaginated into the peritoneal cavity, 

 so as to form a deep infra-frontal recess, a rudimentary mouth and buccal cavity, open- 

 ing anteriorly and ventrally, having at its bottom the peristome, — a disposition 

 unexampled anywhere else in the whole class, an incipient feature approximating to 

 what obtains in worms. Posteriorly the body, in most of the species, terminates in a 

 caudal prolongation, and tlien the periproct is subdorsal, as among the Cassididida^, 

 or at least posterior; in one species, Echinocrepis cuneata, the body is simply pointed 

 behind and the periproct subventral. The stomatoproctic axis is nearly parallel to 

 the ventral plane. 



The bilateral syjnmetry of tlie constituent elements is highly developed, while, at 

 the same time, the dorsal side contrasts with the ventral in a strongly marked man- 

 ner. In these points the Poiirtalesiada3 de])art frdin tlie Archieonomous type more 

 widely than any other group. 



The three skeletal systems, forming together an unbroken surface, are all pro 

 seiit, in different states of development: the p(!risomati(! system predominates; the 

 and)u]:icral presents its five rays, while the cahcinal sxsteni is seen to lose its character, 

 and to \'erg(' upon deca}'. 



