FOSSILS OF THE BURLIXGTOX GKOUP. 367 



arms removed, though they seem generally to have a smaller number 

 of arms, which are also generally longer in proportion, and a rather more 

 excentric ventral tube, or proboscis, which appears also to be more liable 

 to be bent to one side, and is often more or less swollen in the middle 

 and narrow below. 



These two groups (Alloprosallocrinus and Eretmocrinus) should, we 

 think, be at least separated subgenerically from the typical forms of 

 Batocrin us, and may even be found to belong properly to distinct gen- 

 era. We should certainly 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 arms is subject to considerable varia- 

 tion in the degree of its development in the different species, being not 

 very strongly marked in some species, while we also observe some 

 slight tendency to a similar flattening of the upper part of the arms in 

 other types of the Actinocrinidw, such, for instance, as in some species 

 of Dorycrinm, and other forms usually referred, in this country, to Acti- 

 nocrinus. 



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

 note, are entirely confined to America, and,so far as yet known, nearly, 

 if not entirely, to the lower Carboniferous rocks. We give first the 

 names of the species of true Batocrinus, and under separate divisions 

 those of Eretmocrinus and AUoprosaUocrimis. We cannot, however, be 

 positively sure, in all cases, in regard to the separation of the species of 

 the subgenus Eretmocrinus from those of true Batocrinus, where speci- 

 mens showing the arms are unknown. It will also be seen that, even 

 as restricted by the separation, subgenerically, of Eretmocrinus and Al- 

 loprosaUoeriMU) the species referred to Batocrinus are susceptible of 

 division into two sections, that may be entitled to greater prominence 

 than is 'apparent from the specimens yet known. 



1. BATOCRINUS, Casseday. 



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

 20 to 20. Batocrinus icosidactylus and B. irregular-is, Casseday, and B. 

 formosus, B. discoideus, B. papillatus, B. cequalis, B. doris, B. loepidus, B. 

 turbinatns, B. inornatus, B. longirostris, B. calyculm, B. biturbinatus, B. 

 si m His, B. layunculuSj B. mundulus, B. clavif/erusandB. planodiscus, Hall 

 (sp.), all of which were described by Prof. HALL under the name Actino- 

 crinus. Also B. Andreicsianus and B. subcequalis, described by Prof. Mc- 

 CHESNEY under Actinocnnus. Likewise our B. pistillus, B. piatilliformis 

 and B. quasillus. Also B. rotundatus (=Actinocrinus, O. and S.), as 

 well as B. Christyi* and B. KoninckiJ described by Dr. SHUMARD under 

 Actinocrintu. 



* This ia the only species of the whole Batocrinus group known to have two arms springing 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 gradation towards 

 Sretmoenmu. 



