NATURAL SCIENCES OF PHILADELPHIA. 167 



It will therefore be seen that, excepting, in mere specific details, these formu- 

 las, as far as they go, agree exactly. There is, however, a character which, 

 although not apparent in Messrs. Lyon and Casseday's formula, was neverthe- 

 less mentioned in their description, in which the types of these groups differ, 

 that is, in the position of the pseudo-brachial appendages (arms of Phillips 

 and of L. and C.) with relation to the other parts. In Gilbertsocrinus these 

 appendages are placed directly over the arm-openings and above the inter- 

 brachial spaces, while in Goniasteroidocrinus they stand over the interradial spaces. 



There may be various opinions in regard to the value of such a difference, but 

 to the writer it seems of not more than subgeneric importance. If these appen- 

 dages were true arms, or like the arms in other crinoids, designed to support 

 the reproductive organs, (" conceptacula,") little doubt could be entertained 

 in regard to the full generic value of such a difference in their position. The 

 fact, however, that although provided with a central cavity through their entire 

 length, they r have nowhere any external openings, being as it were hermetically 

 sealed, is conclusive evidence that they could have performed no such function. 

 Hence it is probable they should be viewed rather as being in some respects 

 analogous to the lateral branches, or verticils, so often given off from the 

 columns of Platycrinus and other crinoids. This opinion seems to derive sup- 

 port from the fact that, in some of the typical forms of Gilbertsocrinus, as well 

 as in American species of Goniasteroidocriniis, these appendages, at their origin, 

 consist of a double series of pieces, pierced each through the centre by the only 

 cavity they posses, exactly like the joints of a column, or those of its lateral 

 branches, for which latter they might readily be mistaken, if found detached. 



From all the facts it seems probable, therefore, that the only relations these 

 false arms bore to the reproductive system, was that of strong rigid guards 

 thrown off from the margins of the dome, for the protection of the slender, true 

 ova-bearing arms hanging beneath them. Hence, although their existence or 

 absence may be a good generic distinction, ihe'ir position over the interradial, or 

 interbrachial spaces, can scarcely be regarded as such. 



It will probably be remembered that, in a paper read before the Academy by 

 Prof. Worthen and the writer, in September, 1860, and published in the Pro- 

 ceedings for that month, (p. 383), we suggested that a genus proposed by Prof. 

 Hall at about the same time, under the name Trematocrinus, was apparently 

 very closely related to Goniasteroidocrinus, Lyon and Casseday, 1859, and that 

 we should not be surprised if it would prove to be the same. Having recently 

 had an opportunity, through the politeness of Mr. Lyon, to examine good spe- 

 cimens of the typical species of the latter, the writer is completely satisfied that 

 there is not the slightest generic or even subgeneric difference between the 

 types for which these two names were proposed,* and as Lyon and Casseday's 

 name has priority, it will have to be retained for the group, whether we regard 

 it as a genus or a subgenus. It is true the later name is shorter and more 

 euphonious, but we have no right for that reason to make it an exception to 

 the generally accepted law of priority. It is surely not greatly more objec- 

 tionable than Macrostyloerin.ua, Hall, still retained by its author instead of the 

 later name Cytocrinus, Roemer. 



The following are the American species of this group, viz. : Gilbertsocrinus 

 (Goniasteroidocrinus) tuberosus, Lyon and Casseday; Gilbertsocrinus (Goniast.) 

 fiscellus, = Trematocrinus fiscellus, Meek and Worthen ; Gilbertsocrinus {Goniast.) 

 typus, G. (Goniast.) tuberculatus, G. (Goniast.) papillatus, G. (Goniast.) robustus, 

 and G. (Goiiiast.) spinigerus, = Trematocrinus typus, T. tuberculatus, T. papilla- 

 tus, T. robustus and T. spinigerus, Hall. 



* As already stated, it was ascertained from the examination of Mr. Lyon's typical species, that it 

 possesses the same ambulacral openings as the species upon -which Trematocrinus was founded ; 

 and that the slender pendulous "plumose cilia' of Lyon and Casseday (here regarded as true 

 arms) are connected with these openings, as the arms of other palaeozoic crinoids connect with the 

 arm openings, excepting that they hang down, iustead of ascending. 



1865.] 



