2 PROCEEDINGS OF THE NATIONAL, MUSEUM. vou. 61. 



cific value. However, as a record of the first known occurrence of 

 the genus in America, and of the more full exhibition of the stem 

 characters than has been hitherto available, it is advisable to describe 

 it as a new sftecies, for which I propose the name : 



BALANOCRINUS MEXICANUS, new species, 



Plate 1, figs. 1-11. 



Known only from the stem. Stem cylindrical, large, and attaining 

 a great length. A fragment 25 cm. long (pi. 1, fig. 1) , here designated 

 the type, tapers from 12 to 10 mm. in diameter, and the stem from 

 which it was detached was more than 5 meters in length, traces of it 

 having been seen for about that distance in the formation where it 

 occurred. Other fragments range from 18 mm, diameter to G mm. 

 The columnals vary from 2 to 4 mm, in length (relatively shorter in 

 the larger stems), the shortest ones being the nodals, which occur at 

 intervals of 17 to 20 ossicles, and bear strong cirri, either singly or 

 two to each nodal, about opposite. The cirri are long and strong, 

 two of them being preserved in place to lengths of 14 and 15 cm. ; 

 they taper from 4 to 2 mm. and have 48 and 52 ossicles, respectively ; 

 two others, somewhat displaced, are preserved to nearly the same 

 length. 



The cirrus sockets occupy the greater part of two ossicles, the nodal 

 and a shorter supranodal or infranodal, separated by what is doubt- 

 less a syzygial joint, the characteristic structure of which can rarely 

 be seen in the specimens ; it is uncertain which of the two is uppermost, 

 but from analogy with the living pentacrinoids it is probably the 

 longer one, in which case figures 2, 3, 7, and 9 should be reversed. 



The axial canal is circular and very small throughout; it is sur- 

 rounded by five triangular depressed areas known as " petaloid sec- 

 tors" (a term applied to these areas in the genus Pentacrinus^ in 

 which they are elongate and leaf-like), which are fossae for the lodg- 

 ment of ligaments ; these are separated by partitions connecting with 

 the peripheral crenelated band that forms the contact surface of the 

 stem ossicles; the septa are linear and well marked, and they some- 

 times appear as if divided by a median groove. 



The circular area occupied by the ligament fossae varies in size in 

 different parts of the stem ^ from one-third to one-half, or even two- 

 thirds, the radius of the joint face, but usually about one-half. The 

 radiating crenelations which extend continuously around the periph- 

 ery of the joint face form a rather deep band, ordinarily about half 

 the radius in width ; they are usually about 10 to each sector, but are 



1 Springer, On the crinoid genus Scupfiocrinus. Smithsonian Publication 2440, 1917, 

 p. 37, pi. 8, figs. 2-5. 



