246 PROFESSOR ALLMAN ON A PRE-BRACHIAL STAGE 



which we find in the calyx are a large centro-dorsal portion, carrying the articu- 

 lated dorsal appendages, and the five radii, each composed of three radialia, the first 

 of which is directly attached to the centro-dorsal piece, while the third carries two 

 largely developed pinnulose arms. There is no trace of basalia, and no trace of 

 the fi.ve triangular roof-plates of the larva. It will be thus seen, that instead of 

 the five minute plates representing the radii in the larva, we have here the radii, 

 consisting each of three well-developed radialia, and constituting the principal 

 portion of the calyx, while the arras totally absent in the larva, are in the adult 

 so developed as greatly to exceed in magnitude the whole of the remaining 

 portion of the animal. 



The composition of the calyx in our pre-brachial Comatula has a special in- 

 terest, when we view it not only in relation to that of the adult, but to that of 

 the typical forms of extinct Crinoidea. Its large and very distinct basalia show, 

 that in this early stage it is not alone in the presence of a stem that Comatula 

 approaches the typical Crinoidea, but that its calyx also, so different in the adult 

 from the calyx of the typical forms, is here constructed upon essentially the same 

 plan as that which we meet with in such genera as Platycrinus, which we may 

 regard as presenting the type composition of this part.* As no trace of distinct 

 basalia can be found in the adult Comatula, these elements must have either 

 coalesced with some of the others in the progress of development, or, what is 

 more probable, have been obliterated l)y the encroachment of the radii and centro- 

 dorsal piece. f 



In the fossil genus Solanocrinus, and in the living genus Comaster, founded 

 by Agassiz for the Comatula multiradiata of Goldfuss, though afterwards sup- 

 pressed by Johannes Muller, as founded on characters which he had not been 

 able to confirm in any living species, we have a Comatula in which five small 

 basalia alternate with the radii, but are not large enough to form a continuous 

 zone, separating the radialia from the centro-dorsal piece. Solanocrinus would 

 thus represent a stage in the development of Comatula before the basalia had 

 become entirely obliterated, and therefore intermediate between the subject of 

 the present paper and the adult. 



A series of highly valuable, but as yet unpublished observations, have been 

 made by Dr Carpenter, on the development of Comatula, in which he has traced 

 the progress of the animal from a very early period after the first appearance of 

 the arms to its final detachment from the stem. • In the earliest of these stages, Dr 

 Carpenter has found the five roof- plates still present, and he informs me that 



* It should be borne in mind, that while the basal zone of Platycrinus appears to depart from 

 the type, by having only three distinct basalia, these pieces easily admit of a further analysis into 

 the typical number five. 



■j" From a letter vehich I have received from Dr Carpenter since the above paragraph was 

 printed, I find that he has instituted a nearly similar comparison between the calyx of the young 

 Comatula and that of the adult typical crinoid. 



