Descriptions of Crinoids from the Upper Suhcarhoniferous. 325 



Dames to the forms herein described at present, the more especially as 

 I have had no authentic examples of the two species above mentioned 

 with which to compare the specimens now under consideration, and 

 must, therefore, rel}^ upon my own interpretation of the descriptions 

 and figures in illustration of the species mentioned. I propose, in this 

 paper, carefully to describe the two species from very perfect ex- 

 amples, and a series of sliced specimens which exhibits all their peculi- 

 arities of internal structure, hoping thereb}^ to place before the students 

 of our subcarboniferous crinoids the fullest possible information about 

 the genus to which these forms unquestionably belong. Dr. Wach- 

 smuth, in the volume above referred to, gives a verj^ full discussion of 

 what he calls the " t3^pical form," and places under it the two species 

 to which reference is made above. It will be seen, if a careful com- 

 parison is made with what is here written, that his general description 

 contains reference to few characters not indicated by the specimens 

 described in this article. If we have, however, a very full and perfect 

 series of specimens, we can not fail to observe that striking modifica- 

 tions of the body accompanj^ the equally striking modifications of the 

 dome, or upper, umbrella-like expansion, covering the distal end of 

 the ventral sac. 



The species to which Dr. Wachsmuth gives the name H. depressus^ is 

 represented on the plate accompanying this article, b}- figures as follows: 

 Fig. 1, side opposite the azj'gous area; fig. 2, azygous side; fig. 3, top 

 of dome, from which the spiniferous marginal plates have been removed; 

 fig. 4, basal view, showing the length of the broken brachial spines; fig. 

 6, vertical section of a specimen through the ventral sac, showing, 

 first, the pores perforating the plates at the sutures; second, at "a" 

 these pores cut across; third, the lower plates of the ventral sac, resting 

 upon an arch of plates which is continued over the cavity of the body, 

 from the inner ventral plates, which may be seen upon the right of the 

 figure cut in vertical section. 



The description of this species may be formulated as follows: no 

 reference being had to its jdentit}' with any species hitherto described 



Hydreionocrinus depressus, Troost (Wachsmuth non Wetherby). 



Under-hasals — Five, small, nearly or quite concealed by the column 

 upon the outside, and forming the base of " a deep concavity" within 

 which the latter is attached; the upper or inner side of these plates is 

 expanded and flexed outward so as to form a portion of the base of the 

 cavity as seen from the inside. 



Basals—¥\\Q, pentagonal, of nearh' equal size, petal like, the upper 



