ECHINOIDEA. I. 6l 



To this genus belongs further one specimen (or inore?| from Chall. st. 272 determined by 

 Agassiz as Phormosoma tenuef — The spicules (PI. XI. Fig. 18) are as in A", asterzas and arranged in 

 the same way; no sucking disk. I can give no information of the fact whether the spines are as in 

 K. astcrias. as I have no notice of this feature. The pedicellarise are very similar to those of FC.asterias, 

 but here moreover a larger form of tridentate pedicellariae is found (PI. XIII. Figs. 15, 21), which I 

 have not seen in the type specimen of K. astcrias. As, however, the pedicellariae agree otherwise so 

 exactly, it may be supposed that this form will also be found in K. astcrias. This larger form of 

 pedicellarise is chiefly constructed as the smaller one; the cover-plate has only a few holes in the 

 median line, or is quite open the edges not joining completely. The point is a little widened, broadly 

 hastate, with exceedingly finely serrate edge; (as in the triphyllous pedicellariae the serrations are only 

 to be seen under very high magnifying powers); the holes in the blade are beautifully arranged in 

 curved series. They are very long-necked; the head up to o-8 mm ; the stalk is of the structure char- 

 acteristic of the genus Kamptosoma. The smaller form of tridentate pedicellariae resemble to a high 

 degree those of K. astcrias the only difference being that the apophysis and edges have no thorns. 

 The triphvllous pedicellariae are somewhat shorter and more arched than those of K. astcrias, but they 

 have the same peculiar cover-plate, and the serrations of the edge are likewise exceedingly slight. — 

 There can be no doubt that this species also belongs to the genus Kamptosoma; but it may be 

 doubtful whether it is a separate species, or identical with K. astcrias. The small differences in the 

 pedicellariae are suggestive of its being a distinct species; but this question cannot be decided with 

 certainty, till a direct comparison of the two specimens has been made. 



Xow we have only left two of the species referred to Phormosoma, viz. Ph. panamense A. Ag., 

 and Ph. hispidum A. Ag. As to the former it has been supposed above that it ma}- be a genuine 

 Phormosoma, of the latter nothing at all can be said. Both species have only been preliminarily and 

 very incompletely described. 



The genus Sperosoma established by Koehler (228, 229) is especially characteristic by the 

 peculiar construction of the ambulacral areas on the actinal side. The secondary ambulacral plates 

 are of about the same size as the primary ones; the primary ambulacral plate is divided into an outer 

 part, in which the pore is found, and an inner part. Thus on the actinal side the ambulacral area 

 consists of 8 series of plates. The tube feet are placed in three widely separated series. The spicules 

 are large fenestrated plates, not arranged in series; there is a well developed sucking disk (PI. XIV. 

 Fig. 4). Only tridentate and triphyllous pedicellariae are found. The tridentate ones (PL XIV. Figs. 2, 

 6, 33) remind somewhat of those in Ph. placenta, especially the small forms are only with difficulty to 

 be distinguished from those; the wideniugs from the upper end of the apophysis do not reach to the 

 edge of the blade. There is a rather coarse net of meshes in the bottom of the blade, slightly devel- 

 oped in the small forms, more developed in the larger ones, and in these latter it is set with thorns 

 (PL XIII. Fig. 12.) The length of the head up to 2 mm , the neck rather short in the large ones; the stalk 

 of the common structure. In the triphyllous pedicellariae the cover-plate is rather slightly developed, 

 with numerous small holes. The edge finely serrate. The primary spines on the actinal side curved, 

 with a large, white hoof. 



Besides the species of Koehler, Sp. Grimaldii, a species established by Doderlein (11S), Sp. 



