1879.] NATURAL SCIENCES OF PHILADELPHIA. 259 



The generic description was made from a single specimen, and 

 this was in several respects defective. Cleiocrinus has, according 

 to Billings, five basals alternating with the radials, and forming 

 with them a belt around the column. Such a structure has never 

 been found in any Crinoid. In the typical specimen, the com- 

 paratively large column conceals from view the lower part of the 

 calyx, a space large enough to accommodate one or two series of 

 plates, and analogy suggests that this may have been the case. 

 The five plates which Billings found alternating with the primary 

 radials, and which he called basals, are certainly interradials ; and 

 as the specimen in every visible character closely resembles 

 Ichthyocrinus and allied forms, we have good reason to suppose 

 that it, like those forms, possessed five small basals and three 

 underbasals, both hidden by the column. The latter were prob- 

 ably very minute and rudimentary, since the specimen is from the 

 Lower Silurian, where it is almost the only representative of the 

 family. This alone induces us to try to define generic characters 

 from a single imperfect specimen. Notwithstanding, therefore, 

 that some of the elements are problematic, we propose until some- 

 thing better is found, the following: 



Revised generic description. Cah-x obconical or pyriform, with 

 bilateral symmetry. Underbasals probably three, minute or rudi- 

 mentary. Basals probably five, very small and hidden by the 

 column. Primary radials three by five, increasing in width upwards, 

 supporting several superior orders of radials all dichotomizing 

 uniformly, and interlocking laterally with those of adjoining rays. 

 Interradials, so far as known, one. Anals four to five, longitudi- 

 nally arranged. G. regius has six orders of radials, the number of 

 plates doubling with each bifurcation, which gives in the sixth 

 order 64 brachials to each ray or 320 to the individual. Whether 

 the small appendages wmich are seen at the top of the specimen 

 were arms, cannot be determined from the figure. 



The only known species is: 



1856. Cleiocrinus regius Billings. Geol. Rep. Canada, p. 276 ; and 1859, Decade 

 iv., p. 53, pi. 5, figs. 1 a-g. Trenton lituest. Ottawa, Can. 



Billings refers to this genus two other species, C. grandis and 

 C. magnificus, which he described from mere fragments of the 

 column, but which we cannot recognize. The fragments may be- 

 long to C. regius, or to almost any other genus. 



