NATURAL SCIENCES OF PHILADELPHIA. 347 



it agrees very closely in the structure of its body, as well as in the number of 

 arm-opening-3 to each ray (that is, four to the anterior and each posterior ray, 

 and two in each of the lateral rays), but at the same time it presents some other 

 differences, that we suspect may be even of specific importance. In the first 

 place it is larger and more robust, atid has a proportionally smaller base, and 

 rather distinctly tumid, instead of even body plates, while its interradial and 

 anal spaces are not near so deeply excavated between the arm-bases as in the 

 type of quinquelobtM. Its third radial pieces also differ in form, being so narrow 

 in all the raj^s as to let the secondarj' radials come in contact with the first 

 interradial and the second range of anal pieces, instead of extending around so 

 far laterally as to separate these pieces. Its vault is likewise more flattened on 

 top. 



In the typical specimen of D. quinguelobus the spines of the vault have all 

 been accidentallj' removed, but in the form under consideration they seem to 

 have been short and stout, though their entire length is not known, as they 

 were apparently broken off during the life of the animal, since they each have 

 the broken end somewhat rounded and indented in the middle. In size and 

 general appearance it is more like D. Mississippiensis of Roemer, but it differs in 

 having rather more tumid body plates, as well as in the number of the arm- 

 openings, that species having four of these openings to each ray all around. 

 It also has a more protuberant anal opening, and probably had much shorter 

 vault spines. It therefore seems to be somewhat intermediate between the J). 

 Mississippiensis and D. quinqtielohus, but is probably distinct specifically from 

 them both. As we have but a single specimen, however, of it, and the typical 

 specimen of D. quinquelobus for comparison, we prefer to place it, for the present, 

 as a variety of that species, under the name inter rnedius, and if it should here- 

 after be found that the differences we have pointed out are constant, it can take 

 the name bj' which we have proposed to distinguish it as a variety, as a spe- 

 cific name. 



Localiti/ and position. — Upper part of the Burlington division of the Lower 

 Carboniferous series, at Burlington, Iowa. No. 164 of Mr. Wachsmuth's col- 

 lection. 



Genus AMPHORACRINUS, Austin. 



As already stated, this group agrees with Actinocrinus in the number and 

 arrangement of the pieces composing the under side of the body, as well as in 

 having the parts adjacent to the arm-bases forming five projecting lobes, 

 distinctly separated from each other by the anal and interradial sinuses. It 

 differs from them both, however, in the structure of the parts above, as well 

 as in having the body generally more depressed, or even flat below, and the 

 vault proportionally more ventricose ; while its second radial pieces are more 

 generally hexagonal than in Dorycrinus. From the latter it also differs in 

 liaving the opening of the vault more or less proboscidiform,* and placed nearly 

 half way between the middle and the anal side, instead of being a simple gene- 

 rally lateral aperture, penetrating laterally a merely thickened protuberance. 

 Tiie proboscidiform extension of its vault, however, is never so long and slen- 

 der as we usually see in Actinocrinus, and also often differs in being crowned 

 with small spines surrounding the very small terminal aperture, which seems 

 always to open upward. As in Dorycrinus, the*\^ault is generally more or less 

 spiniferous, though the spines are differently arranged, and, as far as yet 

 known, never so extravagantly developed as we sometimes see them in that 



* In all the foreign specimens of the typical species of Amphnracrinus that we have seen, 

 only tiie broken base of this sliort proboscis remains ; and this also seems to have bet n 

 the ease with nearly all those from which the published figures which we have had an 

 opportunity to examine, were drawn Cumberland, however, has given a tigure in his 

 Ueliqiiiaj Conservatte, (pi. C), apparently of the typical species amplwra. with the short 

 oblique proboscis well preserved. This will be seen to differ materially from the merely 

 slightly protuberant thickening in which the opening in Dorycrinus is situated. 



1868.] 



