108 PANAMIC DEEP SEA ECHINI. 



in many directions an immense amount of work to be completed before we 

 have a trustworthy guide to the classification of the Echini. 



Among the specimens left at Cambridge, 1 had occasion to examine a 

 specimen (A.gracile?) from " Challenger" Station 169, and am able to give 

 some details and figures of this specimen, plainly showing that it is not an 

 Asthenosoma, but a new species of Phormosoma allied to Ph. hispidum. This 

 specimen measured 24 mm. in diameter, the actinal system 'J mm., and the 

 abactinal 7 mm., with thirteen primary interainbulacral plates, five on the 

 actinal side of the ambitus. 



The actinal system (PI. 51, fig. /) is characterized by the depth of the 

 gill cuts, which are usually barely indicated in many of the Echinothuriaj. 

 There are three and four rows of large actinal plates occupying the whole 

 of the actinal system. The ten primitive buccal plates are more or less 

 elliptical with two to three small secondaries along the actinal edge of the 

 plates, with a couple of minute miliaries adjoining the pores. The primor- 

 dial interainbulacral plate is large, with a projecting lip, on each side of 

 which, adjoining the ambulacra, are the gill cuts; the primordial plates 

 carry from two to three small primary tubercles with the same number of 

 miliaries crowded together in the centre of the actinal part. 



In the abactinal system (PI. 51, fig. -) the proportion of the ocular plates 

 to the genitals is much like that in specimens of Ph. hispidum of the same 

 size (PI. 40, fig. .'). The ocular plates extend somewhat lower along the 

 corona than do the genitals, and the anal plates have only separated the odd 

 posterior genital from the left posterior ocular. The genitals are elongate, 

 pentagonal, the madreporic somewhat larger than the others. None of them 

 are as yet pierced by genital openings. They carry in the center of the 

 plate two or three secondary tubercles irregularly placed, while on the 

 oculars, two or three secondaries, with one or two miliaries, are arranged 

 vertically along the central line. 



The anal system is pentagonal and covered with four or five irregular 

 rows of plates. The larger outer rows are more or less rectangular. The 

 miliary and secondary tuberculation of the ambulacra is coarser than in 

 Ph. hispidum (PL 51, fig. 3), the scrobicular area of the actinal primaries of 

 this small specimen already occupying the whole height of the plate. The 

 greatest width of the ambulacral area is below the ambitus. 



For the sake of a ready comparison of the ambulacra of a Phormosoma 

 and of an Asthenosoma, I have given on Plate 51 figures of Asthenosoma 

 pellucidum and of Ph. zealandioe. 



