FOSSILS OF THE BURLIXCrTOX GROrP. 393 



GEXUS MEGHSTOCKIXUS. O. and 8., 1850. 



Proceed. Acad. Xat. Sci., Phila., 1869, p. 163. 



THE type upon which this genus was founded (J/. Ecansii, O. and S.*) 

 has a short, broad, cup-shaped body, with a depressed vault, aud sides 

 moderately expanded above, and rounded under below to the flat, 

 anchylosed l>a>e, which is usually a little impressed, or less prominent 

 than the first radial and first anal pieces, extending horizontally out- 

 ward all around it so as to form a part of the under side. In some 

 species the base is not properly impressed, though it can rarely be said 

 to project beyond the surrounding next range of pieces. The body 

 plates are moderately thick, and separated by well defined or rather 

 deep sutures, so as to present a more or less convex surface, without 

 sculpturing or radiating cost*, though there are rarely small indenta- 

 tions at the corners of some of the plates. 



The nearly or quite nat vault is composed of unequal, irregular, more 

 or less tumid or convex pieces of moderate size, the middle one some- 

 times rising into a prominent, rather pointed node, that may be in some 

 cases even developed into a short spine. The opening is decidedly lat- 

 eral, often penetrating the anal side beloic the horizon of the arin-ba- 

 sometimes it is on the same horizon as the arm openings, or rarely 

 slightly above them. It is never situated in a thickened protuberance, 

 however, as in Dorycrinus and Agaricocrinus, but always shows thin, 

 broken, abruptly projecting edges, as if, when entire, it had been pro- 

 duced into a short, slender tube, or so-called proboscis, projecting out 

 horizontally backward. 



In the number and arrangement of the pieces composing the walls of 

 the body up to the third radial pieces, inclusive, this genus presents no 

 utial differences from Actinovrinux. with which it also agrees in 

 having the arm-bases more or less grouped, or separated by interradial 

 and anal spaces, and never forming a continuous series all around, as 

 in BatocrinusJ nor an expanded disc, as in Strotocrinus. It not only 

 differs from Atfirwrinns proper, however, in general physiognomy and 

 the nature and position of the opening, but particularly in having its 

 arms each composed of a double series of alternating pieces beloic all 

 the bifurcations, as in Amphoracrimus, from which, however, it differs 

 widely in other respects. The peculiarity of having the arms each com- 

 posed of a double series of alternating pieces beloic as well as above the 

 bifurcations, is not only continued down to the body, but in some species 



* OWES'S Geol. Report. Wisconsin. Iowa and Minnesota, pL 5 a, fig. 3. 



1 We cannot believe that those remarkable truncated forms, with arm-bases in contact all around, 

 and an erect snbcentral proboscis, such as If. *p\not\u. of Lyon (Proceed. Acad. Xat. Sci., Phila., 1861, 

 pi. 4. fig. 7.) really belong to Megistocrinut. 



