THE BEITISH SECONDARY ROCKS. 45 



of the same species, and to some extent also in the same individual. 

 The reason of this is that these rods are not calcifications in a 

 nucleated protoplasmic network like the other pieces of the skeleton, 

 but they are simply formed by a more or less complete deposition 

 of calcareous matter in the five interradial planes around the fibres 

 of connective tissue which effect the synostosis of the centrodorsal 

 piece with the pentagonal base of the calyx." At the same time I 

 drew attention to the striking resemblance between the basal rays 

 of Actinometra and the basals of Solanocrinios, noting, however, an 

 important point of difference between the two structures, viz. the 

 appearance of the latter on the exterior of the calyx, but the complete 

 concealment of the basal rays, as well as of the rosette, in those four 

 species of Actinometra which I had then examined. 



During the past two years I have dissected the calices of a con- 

 siderable number of Comatulce (26 species), and I have found the 

 basal rays to be always present in Actinometra^ and generally so in 

 Antedon, the European species and Ophiocrinus being the exceptions. 

 I have also discovered that in some few species, both of Antedon and 

 of Actinometra, the basal rays do appear upon the exterior of the 

 calyx, as in the fossil Ant. Eetzii and Ant. semiglohosa. Had I not 

 known from actual examination that these recent species have a 

 concealed rosette, I should of course have regarded the visible ends 

 of their basal rays as the unmetamorphosed embryonic basals, and 

 as homologous with the similarly placed basals of Pentacrinus asteria. 

 This is, in fact, the view which I have expressed with respect to the 

 basals of Solanocrinus ; but the extraordinary resemblance between 

 the calyx of Ant. macrocnenia, from Sydney Harbour, and that of 

 S. costatus has led me to doubt its truth. The question is one of 

 great interest, but is beyond the limits of this paper. I am giving 

 it my best attention, and hope ere long to arrive at a definite con- 

 clusion respecting it. It is sufiicient at present to notice that the 

 existence of basal grooves on the centrodorsal does not necessarily 

 imply the presence of external basals and the absence of a rosette, 

 as is supposed by Schliiter. In some species both are present, and 

 in others only the rosette, so that it is comparatively unimportant 

 whether there are external basals or not in Ant. italica. I imagine, 

 however, that a resette is certainly present, as in all recent Comatidce. 

 I have referred already to the curious differences in the degree of 

 development of the basal rays, not only in the same species, but 

 also in the same individual. These are very marked in some of the 

 new " Challenger" Co7natuIce, which may have three of the rays reach- 

 ing the outer surface of the calyx, while the others are invisible ex- 

 ternally, as in most recent Comatidce. This is a parallel case to 

 Schliiter's specimen of Ant. lenticularis, which has only two visible, 

 and to a new fossil species. Ant. cequimarginata (PL Y. fig. 4 c), the 

 unique specimen of which in the British Museum shows the ends of 

 three or, possibly, four of its basal rays on the exterior of the calyx. 

 I may mention here that these basal rays also appear exter- 

 nally in my single (dissected) specimen of Promachocrimis Jcer- 

 ijuelensis. There are ten radials, five of which, alternating with the 



