12 S. LOVEN, ON POURTALKSIA, A GENUS OF ECHINOIDEA. 



luinc; carefully tlie original specimens of this species, and tlius fully to fonfinu the 

 description given by Neumayu, even on points tbat to him seemed dubious; Pl. XIII, 

 fig. 150 — 162. The ambitus of the test is more or less oval, the relation between 

 length and breadth being as 53 : 50, 48 : 48, 39 : 38. The doi'sal face, almost entirely 

 constituted by the calycinal system, is high and hemispherical, the basis flat, even 

 concave. The antero-posterior axis, which coincides with the longitudinal, is detei-mined 

 by two of the ambulacra, those of the bivium, I and V, being notably closer together, 

 almost adjoining one another, while those of the trivium are more widely separated, 

 and by equal distances. The stoma is large, conformable to the general ambitus, 

 and the peristoma, made up of ambulacral and interradial plates, shoAvs no trace of 

 notches. The ambulacra, all alike and equal, are expanded at the peristome, and, as 

 it were, connected there by a narrow somewhat raised margin, then a little contracted, 

 slightl}' expanding again, while ascending the flanks, and terminating a little above 

 half the total height. Their zones of pores, diverging near the peristome, are simple, 

 the plates being all primary, each bearing near the outer margin a geminous pedi- 

 cellar pore, placed obliquely, the inner perforation being nearer to the adoral margin. 

 Inside the pore there is a hemispherical tubercle, smaller and perhaps wanting near the 

 peristome; the middle part of the ambulacrum is finely granulated. 



Regarding the intei^adia Neumayr thought he observed, in each of them, a single 

 peristomal plate, followed by three plates separated by vertical sutures. This I have 

 verified, fig. 152, 154, the exceedingly fine sutures having been made to come forth 

 distinctly, in all the five interradia of the best specimen, by keeping it immersed in a 

 mixture of spirits and glycerine, a medium that at times is effectual on refractory 

 specimens. The first peristomal plates are single, those of 1, 2, 3, 4 equal in breadth 

 to the ambulacra, that of 5 considerably smaller, all of the same shape, hexagonal. 

 llie single peristomal plate is everywhere followed by three very high, laterally conti- 

 guous plates, extending to the termination of the ambulacra. Of these the middle one 

 adorally almost equals the two lateral, and narrows upwards, while these expand. The 

 first plate is smooth, and bears a single, central, large tubercle; the three second plates, 

 smooth in their flattened basal portion, are each provided with a tubercle somewhat 

 larger than that of the first, the three tubercles making a transverse row, and being 

 connected by a distinct rounded ridge, Avhich limits the basal surface from the ascen- 

 ding flanks. All the four tubercles consist of a hemispherical imperforate mamelon 

 surrounded by a narrow, not very distinct areola. Laterally, and from a little above 

 the tubercles, the Avhole dorsal face is thickly covered with oval or roundish granules, 

 which in the interradials partly assume the appearance of vertical rows. 



This disposition of the plates of the interradia is completely foreign to the Endo- 

 cyclic Echinoids. A single peristomal is a characteristic proper to the Neonomous, 

 — the Echinonei excepted — ; but the triple row following it is Avithout a parallel in 

 the whole class. The peculinr foirna of the middle plate recalls, in a distant manner 

 it is true, what is seen in certain Cystoideans, in which however it is barely possible 

 to find out any attempt at order in the disposition of the plates of the perisome. 



