ICHTHYOCRINIDAE 335 



and a part of the adjoining plates are not. Thus the genus will fall beyond the limits of the 

 Taxocrinidae, but by a very small margin. Upon other grounds its affinities with the Ichthyo- 

 crinidae are so evident as to require little discussion. A glance at figure 4b shows that the base 

 is fundamentally that of the family, and the arm structure is that of the heterotomous section 

 of it. But for the modification of the anal series to a tube instead of suturally attached plates, 

 there would be nothing to distinguish this genus from Dactylocrinus, of which it may be 

 regarded as a successor. Its geological position is in the upper part of the Lower Carbonifer- 

 ous ; the Moscow limestone and the Hurlet bed of Scotland, which furnish its only species, 

 may be correlated with the latest division of the American Lower Carboniferous, the crinoidal 

 fauna being nearer to that of our Kaskaskia than to any other. 



Being thus one of the last survivors of the Sagenocrinidae, the strongly Taxocrinoid 

 character of its anal structure may be interpreted as a degenerative feature, with a tendency 

 to return to the primitive weak anal side. An analogous tendency to weakening of the anal 

 side may be seen in Amphicrinus . 



The fortunate acquisition of a partially disintegrated specimen enables me to throw new 

 light upon the more detailed structures of this form, especially of the tegmen, which is pre- 

 served in a somewhat disturbed condition (PI. XLII, figs. 8a-c). The most striking feature 

 is the beautiful preservation of the posterior oral, the madreporic nature of which appears 

 in the principal figure 811, but in greater detail in figure 80, which is a direct photographic 

 enlargement, accurate to the smallest pore. The calcareous substance of these plates is as 

 perfect as when deposited, white in color, and unchanged by chemical action or contact with 

 the matrix. This posterior oral is very much larger than the others, two of which are pre- 

 served ; they were evidently substantially similar to the orals of Tdxocrinus intermedins. 



It is rather remarkable that while the perisome is perfectly preserved, although consid- 

 erably displaced, I have been unable positively to identify any ambulacra ; in one or two places 

 there is a semblance of alternate arrangement of plates, but nothing so well defined as those 

 found in Taxocrinus and Onychocrinus. Even in the arms where the perisome is intact there 

 are no covering plates, but it seems to form a roof for some small longitudinal grooves 

 (fig. 5&). Some interesting details of articulation and sutural union are shown among the 

 figures. The fossae in general are of the interrupted character found in Forbesiocrinus 

 agassizi; but there was room for large masses of ligaments. 



The genus Synerocrinus was proposed by Jaekel solely on the basis of its heterotomous 

 arm structure, with Forbesiocrinus incurvus as the type and only species. 



Synerocrinus incurvus (Trautschold) 

 Plates XLII, figs, i-p; LXXV, figs. 12, 13 



Forbesiocrinus incurvus Trautschold, Bull. Soc. Imp. Moscow, XL (No. 3), 1867, p. 31, pi. 4, figs. 4, Sa-b, 

 and text diag. ; Kalkbr. von Mjatschkowa, 1879, p. 126, pi. 14, fig. n, pi. 15, fig. 3. 



Taxocrinus incurvus, Wachsmuth and Springer, Revision Palaeocrinoidea, pt. 1, 1879, p. 48. 



Synerocrinus incurvus, Jaekel, Zeitschr. d. deutsch. geol. Gesell. xlix, for 1897 [1898], p. 47. — Bather, 

 Treatise on Zoology (Lankester), pt. 3, 1900, p. 190, fig. in. 



Encrinites stoloniferus, Fischer de Waldheim, Oryctogr. Gouv. Moscou, 1st Ed., 1830, pi. 41, figs. I, 2. 



Encrinites moniliformis, Fischer de Waldheim (in part), Oryctogr. Gouv. Moscou, 2d Ed., 1837, p. 151, 

 pi. 41, figs. 1, 2 {stoloniferus on plate). 



Type of the genus. 



A large species. Crown elongate, rounded below from column facet, ex- 

 panding- upward; widest about IIBr 3 , where average height to width is 1 to 1.4; 

 spread of calyx from base, i to 2.6. Cross-section obtusely quinquelobate ; side 

 outline strongly curved. Base indented, with a very shallow depression entirely 

 filled by the upper columnal. Surface smooth. Medium-sized crown 42 mm. 



