1888.] NATURAL SCIENCES OF PHILADELPHIA. 355 



111 alluding to the symmetry or asymmetry of the calyx, we must 

 consider only the arrangement of the plates in the dorsal cup, as the 

 ventral covering in all crinoids, whether composed of vault or disk, 

 is more or less disturbed by the anus. 



We do not regard it as a good distinctive character that in the later 

 crinoids the basals are generally pierced by interradial canals or 

 grooves in connection with the chambered organ, when not a vestige 

 of them is seen in 3Iarsupites, and similar grooves are found in 

 Catillocrinus, Mycocrinus, Grotalocrinus and many Fistulata. Nor 

 do we think it of much importance that in some palaeozoic forms the 

 first division of the rays does not take place upon the third radial, or 

 that in one or two cases the first radials themselves are axillary, when 

 among Neocrinoids Metacrinus, as well as Plicatocrinus, form excep- 

 tions to this rule. 



Another of Carpenter's distinctions is that in the Neocrinoidea 

 with the exceiDtion of Thaumatocrinus, the primary radials are in 

 contact with one another by the entire length of their sides ; but the 

 fact is that there are also among the Palaeocrinoidea a number of 

 genera, both of the Ichthyocrinidae and Inadunata, in which a 

 similar structure is found. 



Now to the presence of interradials, a character upon which we 

 placed so much importance as separating the older from the later 

 crinoids. We held that interradials were present in all groups of 

 the Palaeocrinoidea, but among the Neocrinoideaonly in Thaumato- 

 crinus. This applies very well to the Camarata and perhaps to all 

 Fistulata, but it is possible that among the latter, in certain Carbon- 

 iferous genera, especially within the Poteriocrinidae, their interradials 

 became resorbed. Interradials are also absent in the Larviformia, 

 if we regard their large ventral plates as orals. We also doubt if 

 the so-called interradials of the Ichthyocrinidae are the homologues 

 of the interradials in the Camarata, but rather regard them as com- 

 parable \yith the unevenly distributed, interradially disposed plates, 

 which occur in some of the Apiocrinidae, and which we take to be 

 lierisomic. 



The so-called interradials of the Apiocrinidae, which occur only in a 

 few species, vary among individuals and are irregular in their ar- 

 rangement. According to De LorioP they are represented various- 

 ly by one or three plates in the lower row, even in the same species. 

 Owing to this irregularity they have been regarded by us as "enor- 



1 Paleont. Francaise, 1st Serie Anim. invertebr., Ciinoides, p. 272. 



