1888.] NATURAL SCIENCES OF PHILADELPHIA. 341 



piercing the plate, in a similar manner, and in the same position as 

 the anal opening pierces the deltoid in Orophocrinus, and we could 

 not find on these ground specimens, any indications of another open- 

 ing lower down. These facts led us to the conclusion that the above 

 described opening must be the anus, and that it Avas probably closed 

 by minute pieces as in OropJiocrimis. We think it quite probable 

 that the tubercular elevation which appears in several of the speci- 

 mens, may represent the closed condition, the plates being too smajl 

 to be distinguishable, especially in fossils whose preservation is so 

 peculiar that the suture lines between the large vault plates are 

 often invisible.^ 



So long as the central plate in Haplocrinus was recognized, we 

 saw good reason to believe in the existence of a similar plate in 

 other groups of the Pala^ocrinoidea, especially as a plate similarly 

 situated over the center of radiation was so conspicuous a feature in 

 the vault of many different genera. But after it became evident 

 that no such plate in fact existed in Haplocrinus and allied forms, 

 the idea recurred to us that the plate, so apparently central in 

 many Platycrinidae and Actinocrinidae, might after all be the pos- 

 terior oral, pushed inward to a central position by anal structures, 

 which we had formerly suggested. With the objection arising out 

 of the supposed condition of Haplocrinus removed, this interpreta- 

 tion seemed to us to be one of the greatest force, more likely than 

 any other to answer the conditions of a valid homology, and to 

 obviate the principal objections urged by Carpenter and ourselves, 

 respectively, to other theories. 



Upon comparing the summit plates of the Platycrinidae and 

 Actinocrinidae, it will be seen that the so-called central plate is 

 always inserted between the four large proximals, so that in most 

 cases it occupies, more or less, the center of figure, being enclosed on 

 the posterior side by anal plates, and abutting against them. In 

 Dorycrinus (PI. XVIII, fig. 2), an enormous development of the 

 central plate is shown. In Agaricocrinus (PL XVIII, fig. 3), the four 

 proximals have been separated from it by the intercalation of other 



1 Upon our communicating to Dr Carpenter several months ago our observalions 

 upon Haplocrimis as above set forth, he informed us tliat Prof. Beyrich, of litrlin, 

 had independently discovered the same facts, both as to the construction of the 

 ventr.d pyramid, and tlie location of the opening which we consider to be the anus, 

 and that Beyrich also regards this as the anal opening, while he (Carpenter) thinks 

 it an open question whether it be the anus or a water pore, in which latter ca^e 

 the anus would remain undiscovered. 



