ORGANIC DEPENDENCE AND DISEASE 



69 



case of such attachment to determine its casual or its in- 

 tentional nature. It is in the Devonian that the growing 

 abundance of the crinoids amid legions of Capulus begins 

 to provide us with increasing instances of fixation of the 

 latter to the former. The earliest of 

 all these and the most striking case on 

 record at all, is the combination of the 

 crinoid Melocrinus micmac Clarke with 

 the capulid snail Orthonychia tortuosa 

 Hall from the fauna of the Lower Devo- 

 nian Grrande Greve limestone of Gaspe. 

 Here we have a small species of Melo- 

 crinus overwhelmed and borne down 

 by a massive trumpet-shaped limpet, 

 whose very weight must have toppled 

 the crinoid over to the sea bottom. The 

 aperture of the shell fits down over the 

 entire dome of the crinoid naturally 

 covering the eccentric aboral aperture. 

 The attachment of the shell must have 

 begun very early and continued firmly 

 to the full maturity of the shell, Or- 

 thonychia is a division of almost conical 

 or slightly twisted capulids, the spire 

 being apical and incipient or altogether 

 absent. Such shells have not before 

 been seen in this attached condition ; 

 they were not adapted to it, for their uncoiled form would 

 make the crinoid so top-heavy that the whole combination 

 would succumb. It is therefore not surprising that this 

 record does not repeat itself,^ 

 Craterocrinus ruedem.anni Goldring is a species as yet 



1 This specimen of M. micmac is the only crinoid ever found in the profuse 

 Grande Greve fauna. It was obtained by the writer from a ledge a half fathom 

 under water at low tide. 



Fig. 55. Melocrinus mic- 

 mac, a Lower Devonian 

 crinoid, embraced and 

 almost overwhelmed 

 by a trumpet-shaped 

 snail. 



