582 LESKIADAE. 



LESKIADAE. 



Stilifainilv Leskiadae Gray, 1 8.j."j. Cat. Rec Ech. 



No ilistinct subanal or actinal plastron ; a peripetalous fasciole, enclosing 

 slightly sunken petaloid ambulacra. Anal system covered by a small num- 

 ber of plates; actinostome pentagonal, covered by five con verging- plates, 

 Hush with the actinal .surface. 



PALEOSTOMA. 



Leskia (Gray). is:,i. Ann. M;ig. i Bob. 1»i -.. 1880). 



Paleostoma Lov£x, l si; 7. Vetensk. Ak. Forlidl. 



Test ovoid : actinostome ilusli with surrounding parts of the tost; actinal 

 membrane covered by five triangular valves ; actinal and subanal plastrons 

 indistinct ; peripetalous fasciole slightly sinuous. Anus covered by five to 

 eight converging valves, forming a pyramid over the anal system: two large, 

 prominent ovarian openings. (May and Loven have established a distinct 

 family for this interesting genus; it is as yet known only from a few speci- 

 mens, and those described are evidently the young, as Simpson in his notes 

 says. ■• the dead tests of this species (P. mirabilis) show that it grows to a length 

 of three inches." The mere presence of a pentagonal actinostome. Hush with 

 the test, docs not seem sufficient grounds for a separation from the Brissina, 

 any more than the presence of a few anal plate- covering the anal system ; 

 we find a pentagonal mouth. Bush with the test surrounding it, in many 

 young Spatangoids. and in all young Spatangoids we have also lew anal plates. 

 Until we know more of this interesting genus it seems unnecessary to make 

 any changes in their systematic position, or suggest any other views than those 

 adopted by Loven and Gray, as this genus may prove to belong to a distinct 

 family among Spatangoids. corresponding to the Arhaciadae among the regu- 

 lar Echini, when we know something more of the adult than the mere fact that 

 in large specimens the anal pyramid is not composed of a materially greater 

 number of plates than in the young. Liitken has already pointed out that 

 the presence of a limited number of anal plates was by no means an un- 

 usual structural feature among Echini. h\ the first part of this Revision I 

 have added two genera to the regular Echini formerly known, with only four 

 or five anal plates. The presence of a limited number of buccal plates, how- 



