138 Zoological Society* 



strange and anomalous though it may seem, being essential to its 

 nature and of original design. 



" For assuming that the secretion of a ventral plate may be ex- 

 cited by some accidental jjosition of an individual of a species not 

 commonly possessing such plate, it would be an extreme h3'pothesis 

 to attribute to the consequent abrogation of the locomotive power a 

 gradual and progressive elongation of the head, during successive 

 endeavours on the part of the imprisoned mollusk to attain whatever 

 food might come within its reach. 



" And admitting that, the supplies of food being casual and scanty, 

 the nutriment would require to be longer retained and more com- 

 pletely assimilated, to conclude that the aUmentary canal thereupon 

 acquired additional convolutions, would be still more hazardous. 

 But when we find that, the demands upon the respiratoiy actions 

 being much diminished after the loss of locomotion, the branchial 

 apparatus does not merely present an atrophied state of its usual 

 structure in the free Calyptreeida, but a different condition of that 

 structure, — two very short gills replacing one very extensive one, 

 and the form of the branchial filaments being quite different, — the 

 conclusion seems unavoidable, that the Lithedaphus is a good and 

 constant genus, created with reference to that peculiar mode of life 

 to which its bivalve shell and other generic characters as a Calyp- 

 traeidan are correlated." 



The next paper read was also from Prof. Owen, and contains an 

 account of the anatomy of the Pholadomya Candida. The genus 

 Pholadomya was founded by G. B. Sowerby, upon certain peculiarities 

 observable in the structure of a shell which in some of its characters 

 approaches the genera Solen, Pholas, and My a. The animal exhibits 

 the ordinary characters of the Acephala inclusa of Cuvier, being 

 everywhere shut up in a mantle which gives issue only to the siphonic 

 tube and the foot ; it presents, however, in addition to the pedal and 

 the two siphonic apertures, a fourth orifice, at the under part of the 

 siphon, which is of small size and circular form. This orifice alone, 

 observes Prof. Owen, is sufficient to distinguish the present mollusk 

 from any known genus of the Inclusa. It would seem to be an inlet 

 for respiratory currents, supplementary to the ordinary ventral siphon. 

 The animal, compared with that of the Panopcea australis, the cha- 

 racters of which are detailed by M. Valenciennes, is distinguishable 

 not only by an accessor)' bifurcate foot and valvular aperture, but 

 by its undivided branchite and some other less marked characters; 

 nevertheless the affinity to Panopcea, as indicated by the hinge of the 

 shell, is illustrated by a closer general resemblance of its soft parts 

 to that genus than to Mya, Solen, or Pholas. These two papers, 

 from the pen of Prof. Owen, and of which the above is a brief abs- 

 tract, are illustrated with beautifully executed drawings. 



Dr. PfeifFer's descriptions of new species of Shells collected by 

 H. Cuming, Esq. in the Philippine Islands, were then read. 

 Helix cromyodes. Hel. testa imjier/oratd, depresso-^ 



1 



