Wood — Crinoidfrom the Hamilton of Charlestown, Ind. 297 



Art. XXXI. — A new Crinoidfrom the Hamilton of Charles- 

 town, Indiana ; by Elvira Wood. With Plate Y. 



The following paper was prepared in the laboratory of the 

 G-eological Department of the Massachusetts Institute of 

 Technology : the specimen having been furnished for study 

 through the courtesy of that institution. I take pleasure also 

 in expressing my indebtedness to Prof. William H. Niles, 

 head of the Geological Department, for the opportunity thus 

 offered. 



The specimen which serves as the type of the species 

 described below, although deprived of the free arms and the 

 column, is exceptionally well preserved, showing the more 

 delicate structural features of the test. It is now in the collec- 

 tion of the Massachusetts Institute of Technology. 



Gennceocrinus cari?iatus, sp. no v. 



Calyx sub-globose. Arm regions prominent with deep fur- 

 rows between them. Surface ornamented by delicate, sharply 

 elevated carinse and acute spines. 



Basals three, pentagonal. The five hexagonal radials fol- 

 lowed by 2x5 costals. First and second costals slightly, if at 

 all, smaller than the radials. Distichals 1 XlO. Of the pri- 

 mary palmars immediately following the distichals, that nearest 

 the median line of the ray is an axillary plate bearing 3x20 

 secondary palmars ; the outer is followed by two additional 

 primary palmars, making 1x10 on the inner, and 3x10 on 

 the outer side of the ray, or forty primary palmars in all. 

 Interpalmars three, following one another in vertical succes- 

 sion. The third, or most distal, primary and secondary palmar 

 in each row gives rise to an arm making six arm bases in each 

 ray. The free arms are not preserved. First interbrachial 

 plate followed by two in the second and three in the third row. 

 Plates of the fourth row are variable in number. The suc- 

 ceeding plates merge into those of the tegmen. 



The heptagonal primary anal of the posterior area is suc- 

 ceeded by three plates and these by four with a minute tri- 

 angular plate intercalated between the two rows. Beyond this 

 the plates are irregular in shape and difficult to distinguish, but 

 there are probably five plates in the fourth and three in the 

 fifth row, as represented in the diagram (fig. 1). 



Tegmen moderately elevated, made up of small irregularly 

 arranged plates. Ambulacral regions convex and separated by 

 deep sulci extending half way to the summit of the tegmen. 

 Just in front of the arms in line with the center of the ray is 

 a strong spine 3 to 4 mm long. Immediately surrounding this 



Air. Jour. Sci.— Fourth Series. Vol. XII, No. 70. — October, 1901. 

 21 



