Vol. 56.] AND CICEROCKINUS. 271 



Catillocrinidae, and Haplocrinidse, and that the particular Pisocrine 

 arrangement was so natural a development from that of Heterocrine, 

 that it would not, of itself, serve to distinguish the family Piso- 

 crinidse. On the other hand, the Pisocrinidse, Catillocrinidse, and 

 Haplocrinidse all possessed unbranched non-pinnulate arms, while 

 the arms of all Heteroerinidae and Calceocrinidse were branched on 

 a definite plan. The variation of arm-structure in Pisocrinidse and 

 Catillocrinidse consisted solely in the gradual addition of unbranched 

 arms, borne by small additional radials (pararadials). The variation 

 of arm-structure in Heterocrinidse and Calceocrinidse consisted solely 

 in a gradual advance, along definite lines, from isotomy to hetero- 

 tomy, with the eventual production, in such a form as Ectenocrinus, 

 of a bifurcated arm with ramuli along the sides of the rami, and 

 with brachials forming syzygial pairs. Such a structure was abso- 

 lutely removed from that of any Pisocrinid, but was, the speaker 

 gathered, that of this new Silurian genus, which therefore fell into 

 its natural position as the climax of the Heterocrinidse. 



Turning to the suggested new Carboniferous genus, Mr. Bather 

 said that he felt unable to accept it. The proposed type-species had 

 long been known; the attention of Wachsmuth & Springer had 

 been specially drawn to it, and they had expressly retained it in 

 Platycrinus, saying that ' a similar structure, in a less degree, is 

 to be observed in a few American species.' The species was also 

 connected with various British species, described and undescribed, 

 showing no gap between it and ordinary Platycrini. It was hard 

 to grasp what the Author intended as the diagnostic character. The 

 presence of supplementary plates between the two main arm- 

 branches was a feature of some interest, but the Author had rightly 

 refrained from attaching importance to it. The abstract in their 

 hands only mentioned - the incorporation of the costal and distichal 

 plates in the calyx,' a feature shared by many species of undoubted 

 Platycrinus in both Europe and America. He understood, however, 

 that the Author wished to take for his criterion the abutment 

 of the costal (primibrach) on interbrachials. But this character 

 could also be seen in such similar species as Platycrinus punctatus, 

 PI. expansus, and PI. tuberculatus, not to mention such dissimilar 

 species as PI. spinosus, PI. mucronatus, and PI. coronatus. To 

 speak of an ' annectant form uniting the Melocrinidae and the 

 Platycrinidse ' was to ignore time as well as structure. 



The Author remarked that, as regards the new Silurian genus, 

 the issue was very simple, until it became obscured amid the foliage 

 of a genealogical tree. The calyx presented not merely a general 

 but a precise resemblance to that of Pisocrinus, the arms could be 

 compared with those of more than one genus of Heterocrinidse. If 

 chief stress be laid on the calyx, then the new genus is a Pisocrinid ; 

 if on the arms, it is a Heterocrinid. But the arms of crinoids, 

 being organs of the highest physiological importance, are highly 

 variable and less suited for broad distinctions in classification than 

 the calyx. If this new genus could only be attached to Mr. Bather's 

 1 tree ' by the arms, it would be a misfortune for the ' tree.' 



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