122 [Senate 



these parts in any ScatiSiactory manner to produce a symmetrical body. During 

 this period, I have obtained some, and seen other plates of similar character; till 

 I came to know the existence of such forms from the Niagara group to the Carbo- 

 niferous limestone inclusive. These plates are so perjuliar in shape, proportions and 

 convexity, that, when once attention is directed to them., a single one is sufficient 

 for the determination of its relations. 



It has been only during the past year, that I have obtained the means for a 

 proper description of the genus; and it is now easy to see why all our previous 

 knowledge of these fossils would not suffice for a reconstruction of the body from 

 the separated plates. The bod}"- is unsymmetrical; the column is not attached to 

 the centre in a line with the axis in its ordinary position, but on one side; and the 

 body has not grown erect upon the column. 



From the unsymmetrical form, the peculiar arrangement of plates, the position 

 of the column, etc., I have found myself obliged to employ some diiferent terms 

 from those in ordinary use; and to designate one side of the fossil as the dorsal, 

 and the opposite as the ventral side. The dorsal side is covered by several plates of 

 peculiar shape, some of them closely anchylosed, and presenting the characters of 

 the back of a jacket or tunic in the arrangement of the parts. These plates bend 

 over at the sides, and unite with a few smaller plates, which form the ventral wall. 

 The ventral side consists of one plate, and sometimes of two anch3dosed plates, 

 forming an arch over the space below. This arch is filled by the single triangular 

 or semioval basal plate, which is attached to the dorsal plates by a free joint, and 

 was capable of a great degree of motion when the animal was in a living state. 

 The arms are peculiar, and are as well marked as are the plates of the body by 

 the generic characteristics. 



The whole fossil has so much the appearance of a skeleton hand, that I propose 

 the name Cheirocrinus; of which genus I already know at least five or six species. 



GENUS CHEIROCRINUS (n.g.). 



Base consisting of a single subtriangular or semioval plate, which is composed of 

 three anchylosed pieces (perhaps sometimes of five pieces). The column is at- 

 tached at the lower angle of the basal piece, sometimes within the margin, and 

 sometimes extending to the limit of the plate. Body above the base composed of 

 five or seven pieces, of which two are much the largest. The lower dorsal plate, 

 or first plate above the base, is usually triangular (sometimes narrow or linear), 

 supporting on its upper sloping edges two large plates, which I designate the 

 dorso-lateral plates; and upon the concave line made by the upper margins of 

 these two plates rests the upper dorsal plate, which supports the plates of the 

 dorsal arm. 



These two dorso-lateral, and the upper and lower dorsal plates, are often so firmly 

 anchylosed together as to present the appearance of a single plate, the surface 

 indicating more or less distinctly the lines of suture. The dorso-lateral plates form 

 the dorsal and lateral walls of the body; and their central angles, on the ventral 

 face, are sometimes extended for a little distance between the ventral arch and 

 the succeeding plate The ventral side consists of an arch, which may be of one 

 or two pieces, joining above, and leaving an arched opening below which is filled 

 by the reversed basal plate. Above the dorsal arch, there may be one or more 

 simple plates. The lower sloping faces of the dorso-lateral plates border the two 

 sides of the arched ventral area or opening; while the upper sloping sides sup- 

 port brachial plates and the lateral arms, which may be simple or subdivided. 

 The dorsal arm extends directly in line with the axis; while the lateral arras, 



