348 . HOMOLAMPAS FRAGILIS. 



Homolampas fragilis 



! Lissonotus fragiUs A. Agass. 1869. Bull. M. C. Z., No. 9, I. p. 273. 

 ! Homolampas fragilis A. Agass., 1872. Rev. Ech. Pt. I. 



PL XVII. f. 13-21. 



Test thin ; from above heart-shaped, elongate (PL XVII. f. 15). Seen in 

 profile (PL XVII. f. 14), it is regularly arched anteriorly from the lower side 

 to the apex, running then almost horizontally, and abruptly bevelled at the 

 posterior extremity. The ventral plastron is small (PL XVII. /'. /.;), trian- 

 gular, surmounted by an elliptical subanal fasciole (PL XVII. f. 19), sur- 

 rounding the anal plastron, which projects like a rounded keel below tbe anal 

 system. The spines of the lower surface are large and few in number, eon- 

 fined entirely to the edge of the test, leaving broad, bare bands in the 

 ambulacra! areas and adjoining parts, while on the rest of the test the tuber- 

 cles are minute, carrying small, fine spines, with tbe exception of three large, 

 crenulate tubercles (PL XVI. f. Si), surmounted by curved spines (Lovenia- 

 like) placed near the edge, in the anterior extremity of the test (PL XVII. 

 f. 17). The tubercles are also somewhat larger on the sides of the anterior 

 groove, and more closely packed in the posterior interambulacral space, 

 from the apex to the anal system, than in remaining parts of the test. 

 The plates of the two posterior ambulacra arc comparatively broad, while 

 all the other ambulacra are made up of smaller plates. The actinal system 

 is pentagonal, the mouth is placed near the posterior edge (PL XVII. f. It;). 

 The tentacles of the phyllodes are represented in different stages of de- 

 velopment in PL XVII. f. JO. The portion of the poriferous zone extend- 

 ing from the phyllodes to the apical system is made up of simple pores, one 

 for each ambulacra! plate, so that the ambulacra! areas, seen from above, 

 are scarcely perceptible, marked only by the somewhat more closely packed 

 minute tubercles (PL XVII f. 18) covering the ambulacra! plates. There 

 are three large genital openings ; the right anterior one is obliterated. 

 The anal system is transversely elliptical (PL XVII. f. 1:1), its membrane 

 is covered by minute granulation ; an indistinct branch of tbe subanal fasciole 

 extends along the lower side of the opening ; the anus itself opens in a 

 delicate tube, similar to that of Neolampas. hut shorter, frequently forming 

 a mere lip. The whole test is mottled with dark spots ; the ground-color is 

 grayish, with a purplish tinge. 



From 320 to 368 fathoms. 



