INVERTEBRATES. 195 



Heuce we can scarcely doubt tljat these specimens both really belong to the 

 species described by Prof. Hall, with which Mr. Wachsmuth's specimen also 

 agrees in the number and arrangement of its aDal and interradial pieces. 



Mr. Wachsmuth's specimen shows it to be a noble species, attaining a length 

 from the base to the summit of the vault, of 2.50 inches; while its dilated 

 summit, must have measured, when entire, nearly 3 inches in breadth, and 

 that of the body just below, about 1.80 inches. Its vault is almost perfectly 

 flat, and seems to be provided with a small, nearly central opening. The num- 

 ber of free arms must be very great, though no specimens we have seen are suffi- 

 ciently well preserved to show their exact number. Prof. Hall says there are 

 seventy-two in the entire series. 



As may be seen from our figures, this species closely resembles in form, and 

 the arrangement of its plates, as well as in its surface markings, a species de- 

 scribed by Prof. McCoy, under the name A. costus, from the Carboniferous 

 rocks of Ireland, (Synop. Carb. Foss. Ireland, pi. 26, fig. 2). It is rather more 

 attenuate, however, and has a more protuberant and more truncated base, while 

 it is very improbable that the Irish species (the upper part of which is 

 unknown) has the dilated summit of the group to which the American form 

 belongs; at any rate no European species showing the characters of that type, 

 has yet, so far as our knowledge extends, ever been found. 



Locality and position : Burlington, Iowa; Burlington limestone, of the Sub- 

 carboniferous series. 



Genus STEGANOCRINUS, M. and W. 



(arsyavoQ, covered; xpcvov, a lily; in allusion to the covered free rays.) 



Synon. — Actinocrinus (sp.), Hall, 1858. Iowa Report, vol. i, part 2d, p. 577 and 582; 

 Meek and Worthen, Sept., 1860. Proceed. Acad. Nat. Sci., Philad., p. 387; 

 (not Miller, 1821.) 



Generic Formula. — 



Basal plates, 3. 



Subradials, 0. 



Radials, 3 -(-5. 



Interradials, 3 to 6 (or more?) -f-4. 



Anals, 3 to 10 or more. 



Rays, from the third primary radial pieces, forming greatly produced, free, 

 arm-like appendages, either bifurcating or simple, which are covered, their 

 entire length above, by small plates, and provided on each side with a row 

 of alternating true arms. Vault, with a subcentral proboscis. 



