ICHTHYOCRINIDAE 267 



In 1878 Wachsmuth and Springer, 1 in a paper on Transition Forms in Crinoids, dis- 

 cussed the genus in relation to some newly discovered Lower Carboniferous specimens which 

 agreed with it in a striking manner in everything except that they had well developed inter- 

 brachial plates. For this reason we felt compelled to modify the conception of the genus 

 theretofore obtaining so as to include such forms as these. Inasmuch as the author of the 

 genus had not given a diagnosis from which any exact limits could be determined, it was 

 apparent that its definition was a mere outgrowth of the individual opinions of the subse- 

 quent writers who had treated of it. Having as we thought found the above modification 

 an imperative necessity consequent upon the discovery of new material, we were in turn 

 much perplexed by the fact that this would leave the three genera, Ichthyocrinus, Taxocrinus 

 and Forbesiocrinus, without any very essential structural differences to separate them, and we 

 found no way out of the dilemma except to consider Taxocrinus and Forbesiocrinus as 

 subgenera. 



Further consideration, however, in our Revision of the Palaeocrinoidea, pt. 1, p. 43, led 

 us to recognize the distinctness of the three genera for reasons there pointed out, but we still 

 retained the species with interbrachials (/. nobilis) under Ichthyocrinus. The specimens of 

 this Lower Carboniferous species then known to us did not disclose the anal side, which we 

 still supposed to be not distinctive ; and in the generic description given by us in the Revision, 

 in addition to the three " underbasals," five basals, and details of radials and arms there 

 stated, we noted the " almost equilateral pentamerous symmetry " of the body ; and added 

 " the most striking feature of this genus, by which it is easily recognized, is its symmetrical, 

 equilateral figure, and this pervades the whole body." 



In addition to the foregoing it had then been discovered and pointed out by us {op. cit., 

 p. 31) that in this genus, in common with several others, the plates of the calyx and rays 

 were joined together by a peculiar loose articulation, producing a flexibility in the calyx 

 which sharply distinguished this association of genera from the other crinoids, and caused 

 their separation as a distinct family then called Ichthyocrinidae, but afterwards extended by 

 us into a grand division under the name Articulata, 2 for which Von Zittel 3 afterward sub- 

 stituted the preferable term Flexibilia. 



The foregoing definition of the genus was followed substantially by Weller 4 and by 

 Bather ; 5 but Von Zittel 6 still adhered to the exclusion of interbrachials. 



Until that time the distinctive conception of the genus as usually held — aside from the 

 pliant calyx and abutting arms — was that of a crinoid with perfect pentamerous symmetry in 

 the calyx. The discovery by me of more perfect specimens of /. nobilis, however, disclosed 

 the fact that this species has a perfectly distinct anal side, with plates in a tube-like series 

 like Taxocrinus; and on this account in 1902 7 I proposed for it a new genus, Parichthyo- 

 crinus. The removal of this species restored the parent genus to its former position with 

 rays in lateral contact, without the intervention of anal and interbrachial plates, and, as was 

 still supposed, with perfect pentamerous symmetry. It is true that Weller, 8 in his redescrip- 

 tion of /. subangularis, had noted the fact that there were " costals two, rarely three, in each 

 ray " ; but that was considered to be a mere irregularity such as was supposed to pervade 

 the whole group, and not as contradicting the idea which until then prevailed that this genus 

 was the simplest of them all, having a perfectly symmetrical calyx without anal or inter- 

 brachial plates, and ranging in this simple form from the Silurian to the Carboniferous. 



1 Proc. Acad. Nat. Sci. Philadelphia, p. 252. 



2 Revision of the Palaeocrinoidea, pt. 3, sec. 1, 1885, p. 6. 



3 Grundziige der Palaeontologie, 1895, p. 137. 



4 Chicago Acad. Sci., Bull. 4, pt. 1, 1900, p. 145. 

 B In Lankester's Zoology, pt. 3, 1900, p. 188. 



" Op. cit, p. 138. 



' American Geologist, vol. 30, p. 96. 

 8 Chicago Acad. Sci., Bull. 4, 1900, p. 146. 

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