158 PROCEEDINGS OF THE ACADEMY OF 



Genus STROTOCRINUS, M. and W. 1866 * 



Extending the genus Strotocrinus so as to include, as already suggested, the 

 Act. ventricosus group as a subgenus, we will have, first, the typical urn- 

 shaped species, such as S. perumbrosus and S. liratus, with the structure of 

 Actinocrinites up to the divisions of the rays, but with the body comparatively 

 long and narrow below, and the secondary and other succeeding supplement- 

 ary radials, brachial and intermediate pieces, connected laterally all around, 

 and spreading out horizontally far beyond the limits of the body, so as to 

 form, with the flat or much depressed vault, a broad, more or less distinctly 

 ten-angled disc, from the margins of which the numerous long, slender arras 

 arise, without bifurcating after becoming free.f Indeed, with rare exceptions, 

 the rays can scarcely be said to bifurcate, properly, after the division on the 

 third primary radials, though each main division continues on out, throwing 

 off alternately on each side brachial pieces in close contact with each other, 

 until, at last, it terminates in a single free arm. Each of the arms commences 

 abruptly as a double series of small alternating pieces immediately on the 

 last fixed brachial piece, without an intermediate series of free single pieces 

 extending entirely across. Some of the species, such as S. perumbrosus, have 

 but a very small simple opening situated subcentrally, or more or less excen- 

 trically towards the anal side, and penetrating the flattened vault obliquely, 

 so as to be directed forward or away from the anal side ; while others, like 

 S. Z/ra/ws, have a long erect, subcentral tube, or so-called proboscis, sometimes 

 recurved at the end. The column is known, at least in the species provided 

 with a proboscis, to be peculiar in being composed of very thin segments, a 

 part of which, at regular intervals, project out beyond the others, and send 

 up and down, at equal distances all around, five external, thickened processes 

 or ribs, apparently as a natural provision to give it strength, without destroy- 

 ing its flexibility. 



Then we have the Act. ventricosus group, which not only agrees with the S. 

 pertwibrosus section of Strotocrinus in having merely a very small subcentral 

 or excentric opening in the vault, without any traces of a proboscis, but also, 

 to a considerable extent, in the manner in which the subdivisions of the rays 

 are given off," but differs in having these subdivisions not in contact so as 

 to form a disc, but divided by narrow interradial, anal, axillary, and some- 

 times interbrachial sinuses, the former of which often extend quite in to the 

 body. The species of this group also diff'er from the typical forms of Stroto- 

 crinus in having the body shorter below the arms, and the vault generally 

 more ventricose, and provided with external furrows radiating from the mid- 

 dle to the anal and interradial sinuses. So far as yet known, the species of 

 this type have rather stouter and less numerous arms than we see in Stroto- 

 crinns proper, but generally more than we see in Actinocrinites. In both groups 

 of Strotocrinus the arms are, as in Actinocrinites, provided with numerous pin- 

 nule, or so-called tentacles, but here they seem to be always armed with mi- 

 nute spines directed more or less obliquely upward from their upper margins. 



From Actinocri7iites the A. ventricosus group not only differs in being without 

 any traces of a proboscis, but in having its ventricose, furrowed vault com- 

 posed of numerous minute pieces; and the divisions of its rays, although not 

 forming a continuous disc as in Strotocrinus proper, not grouped into five 

 lobes. Its arms also differ in never bifurcating after becoming free. For 

 this group we propose the name Pkysetocrinus (^Da-xToc, puffed up ; xpivov, a 

 lily, in allusion to the ventricose vault of the typical species, Act. ventricosus, 

 Hall.)t 



The genus Strotocrinus, as here defined, would include the following spe- 

 cies, all peculiar to the lower Carboniferous rocks of America : 



♦Second vol. Illinois Report, p. 18S, 1860. 



+ Some of the species have as many as seventy to eighty arms. 



J Iowa Geological Report, vol. 1, part PalaeonU, pi. 11, tig. 6, a b, 



[July, 



