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'057 



TERTIARY FAUNA OF FLORIDA 



Choristodon Jonas, Zeitschr. Mai., i., p. 185; Molluskolog, Beitr., p. i, 1844. Type C. 



typicum Jonas, op. cit., p. 185 ; Beitr., pi. 7, fig, 3. 

 Naranio Gray, Ann. Mag. N. H., 2d Ser., xi., p. 38, 1853. Type jV. costata Gray ^ Venus 



lapicida Gmelin; Deshayes, Biv. Shells Brit. Mtis., p. 215. 1853. 

 Lajonkairia Deshayes, Biv. Sh. Brit. Mus., p. 217, 1854; ist sp. Venerupis decussata 



Philippi. 

 Petricolaria Stoliczka, Cret. Pel. India, p. 139, 1870. Type Pctricola pholadifonnis Lam. 

 Claudiconcha Fischer, Man., p. 1087, 1887. Type Venerupis monstrosa (Chemn.) Gray. 

 Gastranella Verrill, Am. Journ. Sci., iii., p. 286, 1872; Rep. U. S. Fish Com., 1871-72, 



p. 678, 1873 (Nepionic stage). Type G. tumida Verr., op. cit., p. 286, pi. 6, figs. 3, 3a. 



In describing the genus Pctricola, Lamarck mentions two described species, 

 one of which was actually known to him from a specimen in his collection, 

 the other he cites from a publication of Retzius. The following year Fleuriau, 

 with the approbation of Lamarck, separated the latter as a new genus, Rupel- 

 laria. The type of the Lamarckian Petricola is therefore the Venus lapicida 

 of Chemnitz and Gmelin, renamed Petricola costata by Lamarck, which sub- 

 sequently received the name of Naranio from Gray. It differs from Rnpel- 

 laria only in having a more rotund form and zigzag surface striation. Lajon- 

 kairia of Deshayes is close to Rupellaria, differing chiefly by more regular 

 radial striation, absence of strong concentric sculpture, and rounded rather 

 than pyriform outline. Choristodon Jonas is a rude Rnpellaria, the original 

 characters upon which it was based being pathological. Jonas supposed that 

 the anterior cardinal in the left or the posterior in the right valve was sepa- 

 rated from its base by a layer of cartilage, and in a certain proportion of the 

 specimens this state of affairs really seems to exist more or less completely 

 developed. A careful study of a large series, however, shows that this con- 

 dition is not normal. The only explanation of its occurrence at all which 

 suggests itself to me is that the tooth in question, from having a sort of 

 pedicillate or constricted base, is very liable to fracture at that point and, if 

 this occurs while the animal is living, the break is repaired, not by the depo- 

 sition of shelly matter but by the secretion of conchioline, which serves to 

 hold the fractured tip in place. At all events I find some specimens in which 

 the shelly matter is perfectly continuous, others in which a circular fracture, 

 not entirely decapitating the tooth, is filled with conchioline, and still others 

 where the entirely detached tip is soldered to the base by a layer of conchio- 

 line cement. The anatomical characters of Choristodon do not differ from 

 those of Rupellaria sufficiently to authorize its separation ; indeed, not more 

 than might be expected between distinct species. Certain species which 



