430 



DR F. A. BATHER. 



§ 273. The Callocystinae correspond with Jaekel's Callocystidae, except that 

 Jaekel includes also Glyptocystis, restricted to the genotype, G. mvltipoi'a Billings 

 (text-fig. 38), which I have placed with Cheirocrinus and its allies in the Glyptocystinae 

 (Bather non Jaekel). Although this results in an awkward difference of nomenclature, 

 the actual difference of opinion is not great. Dr Jaekel so fully recognises the dis- 

 tinction of this species from the rest of his Callocystidae that he has to put it all by 

 itself in a Subfamily characterised by several primitive features : the relatively wide 

 periproct, the large number of pectinirhombs, the simple pentamerism of the subvective 

 system, and the paucity of brachioles. Glyptocystis, he says (1899, p. 277), "is so 

 intimately connected with the younger types of Cheirocrinus, that it is scarcely necessary 

 to suppose the original existence of older connecting-links with essentially different 

 organisation. The transportation of Cheirocrinus larvae from Russia to America might, 



Text-fig. 38. — Analysis of Glyptocystis viidtipora, modified from E. Billings. The deltoids are not 

 known, but the black spot indicates the position of the posterior pore-bearing plate 23. The subvective 

 grooves, which are not shown in the diagram, extend over the surface of the radials and subjacent plates, 

 almost to the base, except the anterior groove on plate 15. 



in my opinion, have exerted an influence quite enough to explain the difference in the 

 organisation of the adults." If, then, we inquire why, in spite of this admittedly inti- 

 mate connection with Cheirocrinus, Dr Jaekel transfers the genus to the Callocystidae, 

 we find the answer in his opinion that the younger representatives of that Family are 

 descended from Glyptocystis, and are connected with it in their characters. The grade 

 of differentiation to which Dr Jaekel alludes as being essentially the same in all these 

 genera is presumably the extension of the subvective system over the thecal plates, 

 combined with the partial or complete suppression of the anterior groove in many 

 genera. I considered this in 1900 (pp. (30, 64), but concluded that the derivation of 

 the Callocystinae from Glyptocystis was " negatived by the different modification of 

 the thecal plates." Let us consider only that point which affords the strongest argu- 

 ment for Prof Jaekel. He justly infers that in Glyptocystis the groove on plate 15 

 (his I" 3) was prevented from passing down the theca to the same extent as the other 

 grooves by the pectinirhomb 15-10. But this is only half the explanation. That 

 pectinirhomb acts as a bar, because it is drawn right across the path ; in other words, 



