214 MR. P. H. CARPENTER ON THE GENUS SOLANOCRINUS 



radials and of one basal ray. The two remaining radials have 

 almost horizontal ventral faces, with the usual radial and inter- 

 radial farrows. In the centre is seen the rosette from which one 

 basal ray extends N.E. -wards, with a shallow excavation at its 

 central end. Its fellow pointing N. has been removed so as to 

 expose the basal groove of the centrodorsal, in which it was 

 received. The side view (fig. 27 a) should be compared with 

 PL IX. fig. 6 c. The different positions of the articular surfaces of 

 the radials in Antedon and Actinometra respectively are then well 

 seen. In the former they are inclined at a considerable angle 

 (fig. 6 c), whereas in the latter they are generally nearly or 

 quite vertical, as in fig. 27 a. Both figures also show the de- 

 scent of the ventral interradial furrows into the interior of the 

 calyx. In Act. lineata (fig. 27 a) they end blindly in the exca- 

 vated central ends of the basal rays*. These parts have a singu- 

 lar resemblance to the basals of Ant. canaliculata (fig. 6 c) ; but 

 I believe the resemblance to be one of analogy only, and not of 

 homology. If the basals of Ant. canaliculata are what I imagine 

 them to be, viz. the original unmetamorphosed embryonic basals, 

 they are homologous, not with the basal rays, but with the central 

 rosette of Act. lineata, which is absent in Ant. canaliculata. 



All the above-mentioned figures of recent Comatulce are es- 

 sentially similar to those on plates IV. -VI. of my Actinometra 

 memoir. Fig. 28, however, represents the calyx of a new and 

 very interesting type, Promachocrinus, the chief novelty among 

 the ' Challenger ' Comatulce. It has ten radials instead of only 

 five ; but there is no corresponding duplication of the rays of 

 the basal star. Only five rays extend outwards from the central 

 rosette to appear externally beneath five of the radials, and they 

 must therefore be regarded as representing the primary interradii 

 of the type. Hence those radial pieces which are not separated 

 from the centrodorsal by basal rays are the original embryonic 

 radials, homologous with those of the other Crinoids and of the 

 five-rayed Starfishes. The five others may perhaps be compared 

 to the additional radials developed in many-armed Starfishes, in 

 which, however, the positions of the five primary rays are not 

 indicated in the adult as they are in Promachocrinus. 



The conclusions to which we have been led may be summed up 

 as follows : — 



1. In all the Jurassic and in some, at any rate, of the Creta- 

 * Compare Actinometra, pp. 97-103. 



