. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Pholas. Fig. 364. these appendages are the first parts of the cardinal teeth. There is one fact which deserves to be insisted on in connexion with this genus ; it is that there are no ligaments found, and that the cardinal edge, folded in upon itself (rentrc svr Uii- ini'nie), is not flattened and placed in the same manner as in the other conchifera. Another circumstance of equal impor- tance to be mentioned is that the processes, of which we have just spoken, are buried in the substance of the animal, and covered with a
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Pholas. Fig. 364. these appendages are the first parts of the cardinal teeth. There is one fact which deserves to be insisted on in connexion with this genus ; it is that there are no ligaments found, and that the cardinal edge, folded in upon itself (rentrc svr Uii- ini'nie), is not flattened and placed in the same manner as in the other conchifera. Another circumstance of equal impor- tance to be mentioned is that the processes, of which we have just spoken, are buried in the substance of the animal, and covered with a duplicature of the mantle which accompanies them as they plunge amid the Peiricola. visceral mass. Without leav- ing the genus Pholas, the cuil- lerons may be seen gradually contracting in their breadths, be- coming shorter, and approaching nearer and nearer to the edge. But if other shells be examined, which obviously form the links of transition from the P/w/iidtt to the , or Petricola, the processes are found to turn upon the edge, to become coherent with it so as to form a salient margin, and by their free extremity to produce a projection (b, Jig- 364). In our opinion the toothings of the' hinge of all the other bivalve shells are produced in the same manner; but with such modifications as rarely admit of those relations being traced which are to our mind obvious in those genera that have just been particularly mentioned. With regard to the vhells of the genera in which the hinge is complicated, of which the cardinal edge is thickened, and the cavity of the hook partly filled by the external layer of the shell, it is difficult to imagine in what manner the suc- cessive growth of the hinge has taken place, and to make out its analogy in point of struc- ture with that of the Petricota pholadiformis and of the Pfiultida generally. To discover this it is necessary to break a great number of the shells, or to make various sections of the edge, when the direction of
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