ME. P. H. CAEPEXTEE OX THE GEXTJS ACTIXOMETEA. 105 



der Saule bildeii " (p. 168). This species, however, is possibly not a Solanocrmus at all, 

 but the head of a stalked Crinoid. 



In both these cases the peripheral ends of the basals appear on the external surface of 

 the calyx, between the centrodorsal piece and the radial pentagon, although the extent 

 to which they are visible is very different. 



The long and narrow prismatic-shaped basals of S. costatus evidently represent 

 the five rays of the basal star of Actlnomctra. The iuterradial elevations on the 

 ventral surface of the centrodorsal piece are marked by five median grooves for the 

 reception of the basals, just like the basal grooves of Actinometra ; and these iuterradial 

 elevations are continued beyond the margins of the radial areas, just like the small 

 processes (t) in some species of Actinometra (PL VI. figs. 14, 15). They correspond with 

 five longitudinal ridges on the outer surface of the columnar centrodorsal which separate 

 the rows of cirrhus -sockets. 



We do not, of course, know whether there was a rosette in S. cuslalns. I am 

 inclined to think that this was not the case, as the central ends of the five basals are in 

 : contact with one another laterally for a short distance, instead of being united by narrow 

 bars forming a basal bridge, as in Actinometra ; and their internal or proximal faces 

 were probably perforated by the opening of a short bifurcating canal lodging the fibrous 

 cords on their way to the central canals of the first radials, as in the closely similar basals 

 iof Pentacrinus asteria. Hence these five basals as a whole would represent the circlet of 

 compound basals in Actinometra, viz. the rosette together with the rays of the basal star. 

 Whether, however, only the united central ends of the basals of S. costatus represent the 

 embryonic basal plates, like the rosette of Antedon and Actinometra, or whether the whole 

 star results from a metamorphosis of the embryonic basals, is a question which must 

 remain in doubt, though the latter is by far the more probable supposition. Apart from 

 the analogy of Pentacrinus, as the peripheral ends of the basal rays extend beyond the 

 margin of the radial pentagon, it is hardly likely that they can be the result of cal- 

 cification in the iuterradial portions of the synostosis between the radial pentagon and 

 centrodorsal piece, as in Actinometra and Antedon Eschrichtii. 



The calyx of the doubtful S. Jvgeri presents a great advance upon that of S. costatus 

 with respect to the development of the basals, which led Pictet L to propose the erection 

 of this species into a separate genus. Instead of being long and narrow, and in contact 

 only by their central ends, as in S. costatus and 5. scrobiculaius, they are broad and wedge- 

 shaped, and in contact along their whole sides, so as to form a complete calcareous disk 

 entirely separating the radial pentagon from the centrodorsal piece. 



This is occasionally their position in Pentacrinus, though there are but few species of that 

 genus in which the basals are relatively so large and complete as in Solanocriuus Jcegeri. 

 In P. asteria, and in the two fossil species P. briareus and P. subangularis, they are 

 small and cuneiform and only in contact by their central ends, just as in S. costatus, so 

 that the greater portion of the radial pentagon is in contact with the top stem-seg- 

 ment. In P. Mulleri they are in contact for about half their length, and then diverge, 

 while in P. Wycille-Thomsoni they are completely united with one another along the 



1 Op. cit. p. 2SS. 



