150 PALAEONTOLOGY OF ILLINOIS. 



2. BATOCRINUS, Cassedav— (Eretmoa-inus, Lyon?) 



a. — Arm bases not separated into groups or projectiug as lobes, but forming a 

 nearly or quite continuous series all around ; body basin-shaped below the 

 arms and about as prominent as the vault ; second primary radial pieces 

 almost invariably quadrangular, and generally wider than long ; body 

 plates often tumid, but never marked with radiating costae; proboscis well 

 developed. 

 Actinocrinus (Baiocrinus) icosidactylus and A. (B.) irregularis,. Casseday ; A. 

 clypeatus, A. formosus, A. sequalis and A. discoideus, Hall, etc. 

 b. — [Alloprosallocrinus, Lyon and CASSEDAY=Conocrinus, Troost.) Only differs* 

 from Batocrinus proper in being flat below the arm bases. 

 A. conicus and A. depressus, Lyon and Casseday ; A. euconus, M. and W. 

 c. — ( Uperocrinus, M. and W.) Differs from Batocrinus proper in having the body 

 below the arms very narrow, and drawn out so as to form a kind of handle 

 to the upper part. 

 Actinocrinus pyriformis, Shumard ; A. pistillus and A.pistilliformis , M. and W. 

 d. — Differs from Batocrinus proper in being sub-globose, or depressed so as to 

 become wheel-shaped ; also, in haviDg its body plates less tumid or quite 

 even, and the base more rounded ; very rarely with the interradial spaces 

 emarginated, so as to give a stellated outline, as seen from above or below. 

 Actinocrinus rotundatus, Shumard ; A. similis, A. inornatus, A. biturbinatus, 

 A. sinuatus and A. planodiscus, Hall; A. Christyi, Shumard; A. sequi- 

 brachiatas and A. Hageri, McChesney; and A. asteriscus, M. and W. 



We are very much inclined to the opinion that the Batocrinus group should 

 stand as a distinct genus, but as it seems to shade into Actinocrinus proper, 

 through section b of that genus, and paloeontologists have generally included it, 

 we have concluded to place it, for the present, as a section, under Actinocrinus. 

 It is worthy of note, however, that it is an American group, and is apparently 

 confined to the Sub-carboniferous rocks. It includes, as we have defined it, a 

 rather wide range of forms, some of which, like our A. asteriscus, if compared 

 without the intermediate links, would seem to be very distinct from the typical 

 species ; and yet such forms shade, by easy gradations, through A. ee.quibrachi- 

 atus, McChesney, A. Christyi, and various less depressed species, into A. rotun- 

 datus, and so on through the whole series, so that there seems to be no suffi- 

 ciently defined break to warrant the division of the group even into well marked 

 sub-genera. 



The genus Actinocrinus, as we have defined it, is readily distinguished from 

 our Stcganocrinus, by the remarkable, greatly extended, free, covered rays of 



exactly the appearance of a naturally simple opening, without any traces of a probos- 

 cis. This we believe to be the case with the specimen of A. Hageri, figured by 

 McChesney. That the difference alluded to, however, could have been thus produced 

 in tho typical Actinocrini, in Strotocrinus and various other genera, no one would for 

 a moment believe, after examining good species. 



