456 ME. p. n. CARPENTER ON THE GENUS ACTINOMETEA. 



while the differences between it and Solano cr inns aa'e so very great 

 that it is difficult to understand how they can ever have been re- 

 garded as belonging to one and the same genus. 



The centrodorsal piece of Comaster is hemispherical : but its 

 margin is not infolded as a broad lip, forming a wide superior ven- 

 tral surface on which the first radials rest. These last bear the 

 axillaries directly without the intervention of any second radials, 

 which are always present in Comatula, and have very narrow in- 

 ferior faces that simply rest upon the thick rim of the hemisphe- 

 rical centrodorsal basin. The infero-lateral angles of every pair 

 of contiguous radials are truncated ; and the spaces left between 

 them when they are in their natural condition of apposition by 

 their lateral faces, are occupied by the five small triangular basals 

 which rest on the rim of the centrodorsal basin, and are visible on 

 the exterior of the calyx alternating with the first radials, just like 

 the peripheral ends of the basals of Solanocrinus costatus. In this 

 species, however, the basals are longish rods of considerable rela- 

 tive width and in contact by their central ends, while in Comaster 

 they are small triangular pieces, from the middle of the inner and 

 lower edge of each of which there arises a tooth-like process in 

 the shape of a small cartilaginous rod extending to the centre of 

 the centrodorsal piece which is grooved to receive it. 



G-oldfuss does not describe any thing that could be regarded as 

 a rosette in Comaster ; and the small triangular basals would seem 

 to be the ultimate condition of the embryonic basal plates, with 

 which they exactly agree in their relative position ; but the re- 

 lations of their central processes are somewhat difficult to under- 

 stand. They can hardly be regarded as comparable, except in 

 their interradial position, to the rays of the basal star of Actino- 

 metra ; for they lie in grooves on the floor of the cavity of the 

 centrodorsal basin, aud are apparently independent of the first 

 radials, which have no extensive area of synostosis with the centro- 

 dorsal piece as in Comatula —while from Groldfuss's account of 

 them they do not seem to be calcified, but to be more of a car- 

 tilaginous nature. 



It is possible that the calyx of Antedon Dubenii, as described 

 by Bohlsche*, may present some points of resemblance to that of 

 Comaster ; for, as in this genus, only two rows of radials are visible 

 externally, and between every two radials of the first row is a 



* " TJeber Actinomeira Benneftii und eine neue Comatula- Art (Antedon Du- 

 bejiii)," Wiegmann's Arcliiv fiir Katurgescliichte, 18G0, p. 1)4. 



