112 THE VOYAGE OF H.M.S. CHALLENGER. 



but from the edge of the test by the imbricating plates wHich cover the whole of its 

 actinal membrane. In this species the imbricating plates are more prominent in the 

 space between the teeth and the ambulacral plates (PL VI.* fig. 8). The characteristic 

 reticulation and pits of this genus are coarser both in the ambulacral and interambulacral 

 spaces ; the spines were mostly broken, but to judge from the secondary ones they must 

 have been proportionally longer and stouter than in the Florida species. The shape of 

 the anal system is not elongate in tlie direction of the axis of the large anal plate but at 

 right angles to it, and the second and third anal plates are comparatively larger than in 

 Trigonocidaris alhida with two vevj minute plates intercalated over the anal opening 

 between them and the small fourth anal plate (PL VL" fig. 9). The abactinal system is 

 ornamented by a prominent ridge, extending round the edge of the ocular plates and 

 across the adjoining genital plates, forming a pentagon with rounded angles round the 

 anal system (PL VI." fig. 9). 



Adjoining the anal system in the middle of the genital plates are placed two or three 

 jDrominent secondary tubercles. This highly-ornamented apical system is in striking 

 contrast to the smooth liare abactinal system of Trigonocidaris albida. The pedicel- 

 lariee resemble those of Trigonocidaris cdbida, but the head is somewhat blunter ; in the 

 single specimen collected they were most numerous close to the ambitus on the abactinal 

 surface. In alcohol the colour of the test and spines of this specimen was silvery white 

 with yellowish suckers on the abactinal side. The actinal side of the test was of a light 

 dirty yellow. 



Station 170. July 14, 1874. Lat. 29° 55' S., long. 178° 14' W. ; 520 fathoms; 

 bottom temperature, 6"0° C. ; rocks. 



Cottaldia, Des. 

 Cottaldia, Des., 1855, Syii. Ech. Foss. 



* Cottaldia forhesiana (PL VI." figs. 15-17). 



Cottaldia forhesiana, Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 203. 



Only a single specimen of this interesting species was obtained from Station 1 73. It is 

 allied to the Tertiary Psammechinus monilis. The pores are, however, arranged in simple 

 vertical rows much as in Temnechinus (PL VI.* fig. 15); the spines of this species (PL 

 VI.* fig. 17) closely resemble those of some species of Salmacis and of Temnechinus. It 

 has, like Temnoj^Ieurus and the allied genera, a large abactinal system, but we find no 

 trace of the indentations, grooves or pits of the above-mentioned genera. The general 

 facies of the test when denuded resembles that of the species often united by Echinologists 

 as Psammechinus \_Echinus, pars] The actinostome is sunken as in Temnopleurus 

 and Salmacis, a character in which it difi'ers from Cottaldia ; it may be best, however, 

 to place it in that genus for the present until we have more material to ascertain its 



