NO. 2038. FOSSIL CRINOID GENUS HOMOCRINUS—EIRK. 477 



The basals are five in number, narrow, and unusually long. Their 

 height is a little more than one-half that of the cup, measuring 0.9 mm. 

 in a specimen having a total height of but 1 .6 mm. 



The radials consist of two simple and three "compound" plates. 

 As usual in such forms, the simple radials are located in the anterior 

 and left posterior rays. The various views of the theca, and the 

 analysis of the cup given in plate 42, clearly show the shape, arrange- 

 ment, and relative proportions of the plates. The r. post. Rs is 

 hexagonal, resting below on the r. post. Ki and the r. ant. Ri, abutting 

 laterally against 1. post. R and r. post. Rs, and supporting on its left 

 shoulder the anal x. r. post. Ri is pentagonal, resting upon the basals, 

 and between r. ant. Ri and 1. post. R. It agrees in shape with the 

 1. ant. Ri. r. ant. Rs is quadrangidar as is also 1. ant. Rs. r. ant. 

 Ri differs from the other inferradials in that it is hexagonal instead 

 of pentagonal, joining as it does with r. post. Rs. The two simple 

 radials are of equal height with each pair of "compound" radials, 

 giving the cup a symmetrical outline. 1. post. R supports on its 

 right shoulder the anal x. 



Of the anal structures nothing is known other than plate x. This 

 is a small pentagonal plate which rests below equally on the right pos- 

 terior superradial and the left posterior radial. Laterally it abuts 

 against and is of equal height with the adjacent first primibrachs. 

 It seems probable that x supported a single series of tube plates after 

 the manner of Ectenocrinus. 



The arms are long, slender, and nonbifurcating. One arm is borne 

 by each ray. There is no evidence of pinnulation. The ventral fur- 

 row, as is indicated by a portion of an arm a few millimeters in length, 

 seems to be closed by a double series of alternating covering plates. 

 The first primibrachs are very short and occupy practically the entire 

 breadth of the radial. Measurements in different individuals give a 

 height of 0.35 mm. for this ossicle. The next succeeding brachial and 

 those following up to fully one-half the length of the arms have a 

 practically constant length of 1 mm. In the distal portion of the 

 arms the ossicles tend to shorten very slightly. An ossicle which 

 probably next preceded the terminal has a length of 0.9 mm. The 

 arms are comparatively tenuous, at about one-half the height of the 

 arm the breadth of an articulation being but 0.25 mm. Each ossicle is 

 widest at its extremities, narrowing slightly toward the middle. The 

 shortness of the first primibrachs in cases where the arms are propor- 

 tionally long or heavy or composed of unusually long ossicles is a 

 feature to be noted in other genera. The first prunibrachs of ad- 

 joining rays of Homocrinus are but slightly separated, and probably 

 when bent inward were in contact laterally. 



The column is round. In its proximal portion and for a distance 

 of about 0.6 mm. it tapers rapidly, maintaining the angle of the lower 

 portion of the dorsal cup, Distad from this point the column main- 



