ICHTHYOCRINIDAE 295 



for the very good reason that it was broken off in his specimen — a fact which does not appear 

 in his restored figure {op. cit., pi. 22, fig. 23), but which is clearly shown by Mr. Liljevall's 

 accurate drawing of the same specimen (PL XXXVII, fig. 1). 



Wachsmuth and Springer x did not recognize Clidochirus, but considered it a synonym 

 of Calpiocrinus, a genus of which no one at that time had a very clear idea. In making this 

 disposition we noted that Clidochirus differed in having " four instead of three primary 

 radials — variations which may be expected even in the same species " — illustrating again 

 the notion which prevailed as to the total depravity of the brachial system in this group, due 

 to a then unrecognized element, the radianal. The genus was also ignored by Von Zittel, 

 both in the Grundzuge and in the Text-Book of Paleontology by Zittel and Eastman. 



Bather - reinstated the genus, placing it in his family Ichthyocrinidae along with 

 Pycnosaccus, Lecanocrinus, Mespilocrinus, Nipterocrinus and Ichthyocrinus; but he did not 

 understand its real structure, and diagnosed it as without a radianal — his main distinction 

 for it being the presence of three anals in a vertical series. 



Angelin's specimen, although imperfect, preserved part of the posterior basal, the anal 

 plates, and the extra plate in the right posterior ray, all of which were correctly brought out 

 in his figure; but at the time of the foregoing opinions the significance of that extra plate 

 was not understood, it being supposed to be a mere irregularity characteristic of the group. 

 The discovery of the fact that the plate is a radianal in its primitive position like that of 

 Ichthyocrinus 3 established for Clidochirus a distinct position among the genera of this 

 group which is easily expressed ; but its family relations are perplexing. It is an intermediate 

 form between the Lecanocrinidae and Ichthyocrinidae. Upon the preponderance of the base 

 and stem characters it agrees better with the former, but as to both of these there is consid- 

 erable variability. 



In most of the Gotland specimens, but not all, the infrabasals are prominent on the out- 

 side ; in some they are concealed by the column (PL XXXVII, fig. 6). Both types of base are 

 found among the American species, and in the two Helderbergian forms the infrabasals are 

 thoroughly withdrawn from the exterior. So also some specimens have a tapering column, 

 while in others it is straight from the calyx down. In view of the instability of these charac- 

 ters we may attach greater weight to the general facies, which is decidedly that of the 

 Ichthyocrinidae, among which I have placed it as a variant or transition form. 



In habitus the genus is strongly similar to Ichthyocrinus, having the same conical expan- 

 sion of the calyx by increase in width of the brachials following small radials ; the radianal 

 is of similar form and like position. But in addition to the large anal plate interposed between 

 the posterior rays, it differs in the usually large basals. 



The construction of the anal area is an extension of the plan of Lecanocrinus; instead 

 of one large plate there may be several, but in each case the distal end is sharply angular, 

 fitting closely by sutural connection to the adjacent rays, which come together above it like 

 an arch. 



The structure of the stem is a further indication of an intermediate position. The 

 proximal columnals are usually not so wide as in Ichthyocrinus; they are short, but with 

 more tendency toward the development of still thinner internodals, and they change into more 

 uniformly long columnals further down, — both of which characters are found in the column 

 of Lecanocrinus. The arrangement of the proximal columnals appears very distinctly in the 

 young specimen of C. pyrnm (PL XXXVII, fig. 2), where the intercalation of very thin 

 ossicles between thicker and wider ones is well shown. 



Clidochirus has hitherto been an exceedingly rare and little known genus, but thanks to 

 the activity of Mr. Liljevall the material for its elucidation has been greatly augmented since 



1 Revision Palaeocrinoidea, pt. I, 1879, p. 39. 



* In Lankester, Treatise on Zoology, pt. 3, 1900, p. 18 



3 Springer, Journal of Geology, vol. 14, 1906, p. 479. 



