CRANIA. 193 



Mr. Hancock, who, at my request, in May, 1859, examined the animal of three or four 

 badly preserved specimens of C. anomala (the only examples then to be procured), has 

 informed me that the impressions a are undoubtedly due to the occlusors, /• to the divari- 

 cators, and that when the former muscles relax and the latter contract, the fluid in the 

 perivisceral chamber will be forced forwards, and thus the valves will be opened a little in 

 front, the action being the same as in Lingula; that v,p, is due to what may be termed 

 the ventral adjusters ; that these muscles form a scar close to the outer border of the divari- 

 cator in the ventral valve ; the other extremities of this muscle converge and pass round 

 the outer margin of the oeclusor, to which they adhere, but Mr. Hancock could not 

 exactly determine how they terminate ; d,p, are considered due to the dorsal adjusters (?), 

 one end of the muscle being attached to the dorsal valve, close to the outer border of the 

 divaricators, the other most probably to the anterior process of the ventral valve. Although 

 this could not be satisfactorily determined, from the very indifferent state of preservation 

 of the specimens, at any rate the fibres of this extremity were firmly united to the inner 

 border of the occlusors. The brachial muscle has both its extremities attached to the same 

 valve (the dorsal), the anterior end to the ventral process, the dorsal close to the outer 

 margin of the oeclusor, with which it blends its fibres ; that the arms are fixed to these 

 muscles, which, perhaps, may be named the brachial. The mesenteric (n) is a flat, thin, 

 membranaceous muscle, binding the dorsal mysentery to the process of the hinge-margin, 

 to which, according to Mr. Woodward, the cardinal muscle is attached ; but we may hope 

 that, before long, Mr. Hancock will have been able to investigate anatomically some well- 

 preserved examples, which may be dredged alive, close to some portions of our Scottish or 

 Irish shores. The oval arms are thick, fleshy, and spirally coiled, the volutions are few, 

 and directed vertically towards the cavity of the dorsal valve, somewhat as is seen in 

 Discina and other genera. We may also notice that the brachial muscle is very closely 

 united to the oeclusor; that it is difficult to distinguish the two in the generality of 

 specimens. 



Dr. Carpenter has stated the structure of the shell in this genus to be widely 

 different from that of Brachiopoda generally, but as still conformable to it in being- 

 penetrated by canals which are prolonged from the lining membrane of the shell, and 

 which pass towards its external surface, these differing, however, from Terebratulae in not 

 arriving at that surface, and in breaking up into minute subdivisions as they approach it. 



Although three so-termed species of British Carboniferous Crania will be here described, 

 C. quadrata is the only well-determined species. Of Crania ? trigonal is I have never 

 seen any other than the original type, and a sight of its interior would be necessary prior 

 to the species being definitely adopted. Of Crania ? {Patella) Bgckholtiana, Dc Koninck 

 = C. vesicularis, M'Coy, I am acquainted with but a single Irish specimen. 



25 



