Note on Loven's Article on " Leskia mirabUis, Gray." 248 



Ophiurans, which is however usually but a single slit, never 

 closed by a system of regularly arranged plates, as is the case 

 with the opening to which the name of genital opening has fre- 

 quently been given among Crinoids. In all other Eehinoderms, 

 the genital openings are mere pores in special plates; and in the 

 Starfishes, for instance, it would puzzle any one to point out the 

 position of the genital openings, or of the anus, even in a speci- 

 men prepared to show simply the calcareous parts, such parts as 

 would be preserved in a fossil. We find in almost all sea-urchins 

 a system of plates arranged, more or less regularly, upon the 

 buccal membrane, but they are usually numerous and small, ex- 

 cept in Leskia, where they are limited to five ; so that it is the 

 exception among living Echinoids to find the mouth protected 

 by a system consisting of a small number of plates. If we ex- 

 amine the anal opening we find, on the contrary, as Dr. Lutken 

 justly remarks, a number of genera in which the anal opening is 

 covered by a small number of plates. This is the case in Leskia 

 itself, in Arbacia, in EcJiinocidaris, in Parasalenia, in several spe- 

 cies of Echinometra, and it is a feature which is common to all the 

 young Echini which I have as yet had the opportunity of examin- 

 ing. In young Toxopneustes, Lytechinus, Toreumatica, Temno- 

 trema, Sphaer echinus, Opechinv.s, we find the anal system covered 

 at first in the early stages by a single plate, as in Salenia, after- 

 wards by three, and then for a considerable period of their growth 

 by five plates, one of which is slightly larger than the others, but 

 presenting in all essential features the same arrangement as the 

 plates covering what I would still consider, in the face of the 

 arguments of Billings, reaffirmed by Loven, tin- anal opening in 

 Cystideans. If we were to take a fossil Comatula, of the type of 

 our common Antedon and Actinoimtra, what proof would we 

 have that in one case the ambulacra radiate pentagonally from a 

 centre to each of the arms, the anal proboscis being eccentric, 

 while in the other case the ambulacra form an open horseshoe- 

 shaped curve, from which the 'ixso, branches are sent into tin; 

 arms, the anal proboscis being situated in the open space be- 



