NATURAL SCIENCES OF PHILADELPHIA. 351 



The species presenting the character of arms described above, agree so close- 

 ly in other respects with the typical forms of Batocrinus, that it is perhaps not 

 always possible to distinguish them from specimens with the arms removed, 

 though they seem generally to have a smaller number of arms, which are also 

 generally longer in proportion, and a rather more excentrix ventral tube, or 

 proboscis, which appears also to be more liable to be beni to one side, and is 

 often more or less swollen in the middle and narrow below. 



These two groups [Alloprosnllocrinus and Eretmocrinus) should, we think, be 

 at least separated subgenerically from the typical forms of Batocrinus, and may 

 even be found to belong properlj- to distinct genera. We should certainlj' be 

 disposed to view the Eretmocrinus group as a distinct genus, if it were not for 

 the fact that the peculiarity observed in the structure of its arras is subject to 

 considerable variation in the degree of its development in the diflFerent sjjecies, 

 being not very strongly marked in some species, while we also observe some 

 slight trndency to a similar flattening of the upper part of the arms in other 

 types of the Acdnocrmidm, such, for instance, as in some species of Dorycrinuf, 

 and other forms usually referred, in this country, to Aclinocrinus. 



Below we add a list of the species oi Batocrinus^ which, it is worthy of note, 

 are entirely confined to America, and, so far as yet known, nearly, if not en- 

 tirely, to the lower Carboniferous rocks. We give first the names of the spe- 

 cies of true Batocrinus, and under separate divisions those of Eretmocrinus and 

 Alloprosallocrinus. We cannot, however, he positively sure, in all cases, in re- 

 gard to the separation of the species of the subgenus Eretmocrinus from those 

 of true Batocrinus, where specimens showing the arms are unknown. It will 

 also be seen that, even as restricted by the separation, subgenerically, of 

 Eretmocrinus and Alloprosallocrinus, the species referred to Batocrinus are sus- 

 ceptible of division into two sections, that may be entitled to greater promi- 

 nence than is apparent from the specimens yet known. 



1. Batocrinus, Casseday. 



Section (a). — Species with arm-openings directed outward. Arms from 20 

 to 26. Batocrinus icosidactylus and B. irregularis, Casseday, and B. forviosun, B. 

 discoidcus, B. papillatus, B. irqualis, B. doris, B. lecpidus, B. turhinatus, B. inor- 

 natu.o, B. longirostris, B. calyculus, B. biturbinatus, B. sirnilis, B. Ingunculus, B. 

 mundulus, B. clavigerus and B. planodiscus. Hall (sp.), all of which were de- 

 scribed by Prof. Hall under the name Aclinocrinus. Also B. Andrewsiarius and 

 B. subsequalis, described by Prof. McChesney under Actinocrinus. Likewise our 

 B. pistitlus, B. pistilliformis and B. quasillus. Also B. rotundatus [^Actinocrinus , 

 0. and S.), as well as B. Christyi* and B. Komncki,f described by Dr. Shumard 

 under Actinocririus. 



Section (b). — Species with arm-openings directed upward, and arm bases 

 usually more in groups than in Section (a). Arms, so far as known, 20. 



B. Nashvillie [^Actinocr., Troost) : also B. laura and B. sinuosus {=Actino- 

 crimis, Hall), B. xquibrachiatus (== Actinocrinus, McChesney), and our B. aster- 

 iscus and B. trochiscus. 



2. Subgenus Eretmocrinus, Lyon and Casseday. 



Species with arms flattened and alate above, and generally numbering from 

 12 to 20. Proboscis or ventral tube excentric, usually slender below, and 

 sometimes swollen in the middle, and more or less bent to one side. Vault 

 usually dei)ressed. Brachial pieces more or less in groups, separated by inter- 

 radial and anal sinuses. 



Batocrinus [Eretmocrinus) magnificus, Lyon and Casseday, and B. [Eretmocr. ) 



* This is the only species of the whole Batocrinus group known to have two arm.s spring- 

 ing from each arm-opening, and this does not arise from a proper bifurcation, as the two 

 arms rest directly upon the brachial pieces, without imparting to them the character of 

 axillary pieces. 



t This species has its arms slightly flattened, but not expanded above, showing a grada- 

 tion towards Eretmocrinus. 



1868.] 



