NATURAL SCIENCES OP PHILADELPHIA. 389 



0-73 inch ; breadth of base, 0-27 inch ; height do., 0'07 ; height from base to 

 anal opening, - 46 inch. 



Locality and position. Same as last. 



Genus FORBSIOCRINUS.* 



Forbsiocrinus ? Norwoodi. Body (as near as can be determined from a com- 

 pressed specimen) obconical, or enlarging regularly upwards from the col- 

 umn ; composed of nearly smooth, rather thick, flattened, or more or less 

 arcuate plates, which are connected by linear sutures. Base small, and ap- 

 parently nearly hidden by the column. Subradial plates rather irregular in 

 form, four of them pentagonal, (one of the sides being very short) and one 

 on the anal side apparently heptagonal, with unequal sides. First radial 

 pieces nearly twice as wide as long, hexagonal and heptagonal, and a little 

 arcuate transversely. Second, third and fourth radials, (and in the anterior 

 ray the fifth, ) all short, nearly of the same size, hexagonal and about twice 

 as wide as long. Fifth radial pieces (sixth in the anterior ray) of the same 

 size as the others, heptagonal, and supporting on their superior sloping sides 

 the secondary radials, only three ranges of which have been seen ; these lat- 

 ter alternate with interradials on each side, and show scarcely any tendency 

 to diverge. (Anal pieces unknown). 



Of the interradials, which are numerous, the first are nearly as large as 

 the subradials, as long as wide, hexagonal, and support three smaller pieces 

 in the second range. Above these four are seen in the next range, in one in- 

 terradial space, which is as far up as they can be counted in the specimen 

 examined, though it is evident from the breadth of the interradial spaces 

 that they must increase in number at the same rate for several ranges above. 



The column is round, comparatively thick at its connection with the base, 

 from which it tapers towards the lower extremity. It is made up of extreme- 

 ly thin segments, which fit together by interlocking crenulations, formed 

 doubtless by distinct radiating strise on their upper and lower surfaces. Its 

 central cavity is subcircular, and nearly equal to one-third the diameter of 

 the column, at a distance of one inch below its connection with the base. 



Named in honor of Prof. J. G. Norwood, of the University of Missouri. 



Locality and position. Near Nauvoo, Illinois. Keokuk Limestone of sub- 

 carboniferous series. 



Forbsiocrinus ? semiovatus. Body below the first bifurcation of the rays, 

 narrow semiovate, a little wider than long, expanding rapidly from the base 

 to the summit of the first radial pieces, above which it widens very gradually, 

 or becomes nearly cylindrical ; composed of moderately thick, smooth, or sub- 

 granulose plates, united by distinct sutures,. Basal plates (as defined in this 

 genus by Prof. Hallf) hidden by the column, if they exist. Subradials (of 

 Hall, basal of Koninck and LeHon), of moderate size, wider than long, three 

 of them on the anterior side pentagonal, the two upper sloping sides being 

 considerably longer than the lateral margins; (the other two unknown), 

 First radial plates on the anterior side, heptagonal, wider than long, the supe- 

 rior truncated edge being longer than either of the others. Second radials 

 smaller than the first, hexagonal, and nearly twice as wide as long. Third 

 and fourth radials, a little smaller than the second, wider than long, and 

 quadrangular, or obscurely hexagonal, excepting in one ray where there are 

 only four pieces, the last of which is pentagonal, or obscurely heptagonal, 

 and supports the arms ; in each of the other two rays seen, there is a fifth 

 piece, which seems to be pentagonal, and supports the arms on its superior 

 sloping sides. (Anal and interradial pieces unknown.) 



* The two species we have here referred provisionally to the genus Forbsiocrinus, will 

 probably be found to possess the characters of Onychocrinus of Lyon and Casseday ; but 

 as we have not yet seen the basal plates of either, we do not feel quite warranted in 

 separating them from Forbsiocrinus, 



tSee Iowa Report, p. 630. 



I860.] 



