166 PROCEEDINGS OF THE ACADEMY OF 



This species is apparently most nearly allied to M. hrevicornis. Hall (sp.), 

 but differs in having a greater number of ranges of brachial pieces included as 

 a jjart of tlie walls of the body, and these pieces wider and commencing as 

 double series farther down. Its opening is also placed decidedly lower even 

 than the proposed species Act. minor, of Hall, being distinctly below the hori- 

 zon of tlie lower edge of the arm openings, and nearly halfway down the side, 

 measuring from the highest part of the vault. Its larger vault pieces, except- 

 ing the middle ones, are also more prominent and pointed. Its body and 

 vault plates are all much more convex, its arm bases stouter, its vault less 

 depressed, and its opening decidedly lower than in M. superlatus, Hall (sp.). 



Locality and position. Upper Burlington beds of the Lower Carboniferous 

 at Burlington^ Iowa. No. 161 of Mr. Wachsmuth's collection. 



Genus DORYCRINUS, Roemer. 



DORYCRINUS CANALICDLATUS, M. and W. 



Body under medium size, cup-shaped below the arms, rather rapidly ex- 

 panding from the lower margins of the first radials to the arm bases. Base 

 extremely short, its entire height merely consisting of the thickness of the 

 plates, subhexagonal in outline, with small lateral notches at the sutures, 

 scarcely projecting below the first radial and first anal piece ; facet tor the 

 attachment of the column occupying about half the breadth of the base, round 

 and rather deeply impressed. First radial plates about once and a half as wide 

 as high, all very nearly hexagonal, there being scarcely any perceptible angle 

 at the middle of those over the sutures of the base. Second radials scarcely 

 half as large as the first, about once and a half as wide as long, and presenting 

 the usual quadrangular outline. Third radials a little wider and shorter than 

 the second, pentagonal in form, and bearing on their upper sloping sides, in 

 the posterior rays, two slightly smaller secondary radials, each of which sup- 

 ports two brachial pieces, thus giving origin to four arm openings to each of 

 these two rays ; while in the anterior ray one side of the third radial merely 

 bears a series of branchial pieces leading to an arm, and its other side a ter- 

 tiary radial, supporting two brachial pieces, thus making three arms to this 

 ray. In both anterior lateral rays each third radial bears on each side two 

 brachial pieces in direct succession, making only two arm openings to each of 

 these rays, or fifteen to the entire series.* 



Anal pieces about eight, below the horizon of the arm openings ; first one as 

 ■wide as the first radials, and a little longer, heptagonal in form, and bearing 

 three smaller pieces in the second range, above which there are five smaller 

 pieces in the third range, connecting with others extending up to the opening 

 of the vault. First interradials nearly half as large as the first radials, hepta- 

 gonal in form, and bearing two smaller pieces in the second range, above 

 which one or two small pieces intervene to separate the brachial pieces, and 

 connect with the vault. 



Vault about two-thirds as high above the arm openings as the height of the 

 body below, provided with a single rather pointed and prominent central node 

 that may be in some instances developed into a short spine. Opening with 

 margins a little projecting and situated in a slightly impressed area above the 

 horizon of the arm openings. 



Body plates convex, separated by deeply canaliculated sutures, and rough- 

 ened by a peculiar shallow pitting over the entire surface, but which is larger 

 and deeper at the edges of the larger plates, to which it imjiarts a slightly cre- 

 nate appearance. The plates of the vault are also defined by the same deeply 

 canaliculate sutures, and roughened by similar pitting to that on the body 

 plates, though they are not convex like the latter. 



As we have not seen the arms of this species it is barely possible that it may 



* Sixteen is probablv the normal number. 



[July, 



