330 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The appearance of the basal rays externally as small, rounded tubercles in the 

 interradial angles of the calyx just above the rim of the centrodorsal is a character- 

 istic feature in certain species, particular^ among the Comasteridae, Thalassome- 

 tridae, and Charitornetridas, in the genera Zenometra and Psafhyrometra, and some- 

 times, though seldom, in Heliometra, Solanometra, Anthometra, Florometra, Proma- 

 chocrinus and Thaumatocrinus. But in many cases they may be comparatively 

 well developed, yet not reach the exterior, or they may reach the exterior in only 

 one or two of the interradial areas. This is particularly the case in species having 

 large centrodorsals. In species with small or resorbed centrodorsals, as in the 

 majority of the Thalassometridas and Charitometridse and in many of the Comas- 

 teridae, they are, if present at all, very prominent in all the interradial angles, and 

 if the centrodorsal becomes during growth much reduced in size, as often occurs in 

 such genera as Comanihus, Comaster, Comanthina, Comaniheria or C'omatvla, it 

 never recedes in the interradial angles beyond the external ends of the basal rays, 

 however much it may recede in the radial areas, so that from this cause a sharply 

 stellate centrodorsal is frequently formed in which the pointed ends of the star are 

 tipped by the external ends of the basal rays. 



Occasionally, through individual variation, the external ends of the basal rays 

 may be very large, as in a small specimen of some charitometrid species from the 

 Philippine Islands, which I have had an opportunity of studying (fig. 414, p. 319), 

 so that they are almost as prominent a feature of the calyx as the basals in Isocrinus 

 decorus, which they much resemble. 



The so-called basals in the well-known case of the recent " Oomatula multiradi- 

 ata" (Comcmtlms bennetti), described and figured by Goldfuss, were merely similarly 

 enlarged basal rays. 



In many fossil comatulids what appear to be true basals are visible on the 

 exterior of the calyx; but I have little doubt that in most, if not in all, of these 

 cases what appear to be basals are in reality nothing but the ends of large and well- 

 developed basal rays, similar to those in the small specimen of a charitometrid 

 species referred to above. Carpenter believed that, as the ends of the so-called 

 basals in certain fossil comatulids project beyond the margin of the centrodorsal, 

 it is scarcely probable that they could have arisen from the calcification of the 

 interradial portions of the union between the radial pentagon and the centrodorsal. 

 But the same thing happens in many recent species, especially among the Thalasso- 

 metridas and Charitometridae, where there can be no doubt of the secondary origin 

 of these structures. In these fossil species the central ends of the five so-called 

 basals are in contact laterally for a short distance instead of being united by narrow 

 bars, forming a basal bridge. From this circumstance Carpenter believed that at 

 least the central ends of these structures are homologous with the true basals of 

 stalked crinoids. The same state of affairs, however, has been found in Promacho- 

 crinus, a near relative of Solanometra and of Heliometra, in which there is no reason 

 to suppose that these contiguous inner ends of the basal rays are true basals. 



In the Pentametrocrinidae and Zygometridae, as well as in some of the Antedon- 

 idae, rounded tubercles are found in the interradial angles of the calyx, which, though 



