NO. 3 ON THE FOSSIL CRINOID FAMILY CATILLOCRINIDAE 5 



MYCOCRINUS Schultze 



Mon. Echin. Eifl. Kalk., 1866, p. 222 (sep. p. no) 



In this genus, as represented by its type species, M. boletus, from 

 the Middle Devonian of the Eifel, the essential structure was estab- 

 lished which characterized the subsequent line, namely, a cup com- 

 posed chiefly of unequal and unsymmetrical radials in contact, two 

 of them much larger than the other three, separated at one end by two 

 of the smaller ones abreast, and at the other end by the third smaller 

 plate, which is somewhat larger than the other two. These radials 

 are greatly thickened at the truncated upper face, which is traversed 

 by curved and radiating food grooves leading to the inner cavity, and 

 connecting at the outer edge with numerous small, thread-like arms, 

 which are borne directly upon the radials, usually one from each of 

 the smaller plates and several from each of the larger, up to a maxi- 

 mum of twenty-five or thirty. This is the generalized picture of the 

 type ; the further details apply to Mycocrinus especially. 



Below the ring of massive radials is an equally massive basal 

 ring, usually protruding as a subglobose knob about half the height 

 and width of the cup, but in one case conical, expanding gradually to 

 the radials. This encloses no cavity, but is solid for its entire height, 

 except as pierced by the nerve canals. It is described as being com- 

 posed of two unequal plates (Schultze, Echin. Eifl. Kalk. p. 222, 

 (Sep. no), and as undivided (Jaekel, Crin. Deutschl., p. 55). Of my 

 specimens of the type species, one has the base undivided, and two 

 have two distinct sutures ; in one of the latter by a strong light a third 

 line of division may be seen in the proper position. I have little doubt 

 that the primary division was into three plates, of which the sutures 

 were unequally obscured by compression or fusion in life, or by 

 chemical changes during fossilization. A division into two unequal 

 plates by sutures standing at an angle to each other, as in Schultze's 

 figure 4a, is mechanically improbable, even in such an anomalous 

 structure as this ; there must have been originally a third. 



Of the radial ring, the three smaller RR have partly straight sides, 

 and a large curved indentation at the upper corners next to the large 

 RR, which have corresponding projections to fit the space. By means 

 of these lateral extensions the large radials, which at the basi-radial 

 suture are but little wider than the smaller ones, are at the upper face 

 at least twice as wide; but as between themselves there is little dif- 

 ference in size. The usual number of food grooves, one for each arm 

 base, upon the large radials is about six, but may be four or seven. 

 thus making the total number of arms from eleven to seventeen. The 



