INVERTEBRATES. 151 



that type; and from our Strotocrinus, by the curious expansion of the summit 

 of the latter, formed by the numerous divisions of the rays (with their inter- 

 mediate pieces), between the third primary radials and the free arms. From 

 Amphoracrinus and Agaricocrinus, it is easily distinguished by the lateral open- 

 ing of the summit, and general physiognomy of these types. From Megisto- 

 crinus, as properly resticted, it can in most cases, be distinguished by the 

 position and nature of the opening of the summit, as well as by the mode of 

 division of the rays previous to giving off the free arms, and by differences in 

 the general physiognomy of the entire body. From Macrostylocrinus, Hall, 

 (Cytocrinus, Roemer), it is distinguished by the having its first anal plate rest- 

 ing down upon the base. From Saccocrinus, with which it agrees in the 

 number and arrangement of its basal, primary radial, and interradial plates, it 

 differs in the irregular manner of the divisions of the rays, and the disposition 

 of their pieces, between the third radials and the base of the free arms in that 

 genus. 



M. M. de Koninck and Lehon, in their valuable work on the Crinoidea of 

 the Carboniferous rocks of Belgium, express the opinion that the genus Actino- 

 crinus is confined to the Carboniferous system. In this country, however, we 

 have evidence of its existence as early as during the deposition of the Upper 

 Silurian rocks; several species are also known in our Devonian series. It was 

 during the Subcarboniferous epoch, however, that it attained its greatest devel- 

 ment, particularly while the Burlington limestone was forming. We know of 

 no species of the genus higher in the series than the St. Louis limestone, and 

 the only two species yet found in that rock, belong to the Batocrinus division. 



Subgenus BATOCRINUS, Casseday. 



Sec. c. (UPEROCRINTTS, M. and W.) 



ACTINOCRINTJS PISTILLIFORMIS, M. and W. 



PI. 14, Fig. 8. 



Actinocrinus pyriformis, var. rudis, Meek and Worthen, June, 1861. Proceedings 

 Acad. Nat. Sci. Philad,, p. 131 ; (not A. pyriformis, Shumard, Geol. Report Mis- 

 souri, p. 192, 1855 ; nor A. rudis, Hall, Sup. Iowa Report, p. 33, 1860.) 



Actinocrinus pistilliformis, M. and W., Aug., 1865. Pro. Acad. Nat. Sci. Philad., p. 153. 



Body, exclusive of the proboscis, pyriform, being very nar- 

 row and apparently cylindrical from the base to the top of the 



