NATURAL SCIENCES OF PHILADELPHIA. 203 



Dr. Gould, in his text, refers to fig. 497 a b t which was not published, in con- 

 sequence, as he informs me, of the only valve being broken while in the artist's 

 hands. 



P. latissima is readily distinguishable from truncata by its posterior 

 side being much shorter, with the edge more rounded, and by the greater thick- 

 ness of the shell in proportion to its length. 



Genus Dactyuna, Gray. 

 Dactylina, Gray, Proc. Zool. Soc. p. 187, 1847. Gray, Ann. and Mag. Nat. 



Hist. 2 ser. viii. H. and A. Adams, Genera, ii. p. 325. Chenu, Man. 



Conch, ii. 

 Daclylus, Pliny, Hist. Nat. ix. cap. 87. 

 Pholas, (partim,) of authors. 



There are two distinct forms of Dactylina ; in the first, which I propose to 

 consider the typical form, the nuclei of the dorsal valves are situated at their 

 outer margins, posterior to the centre ; several impressed lines radiate from 

 the nuclei to the inner margin, dividing each valve into several ciubtriangular 

 spaces. The valves are much emarginate anteriorly, forming a short, wide 

 hiatus. 



The other form may be thus characterized, 



Subgenus Gitocentrum. 

 Nuclei of the dorsal valves anterior, situated nearer the inner margin. Dor- 

 sal plates marked by radiating lines. Valves not emarginate anteriorly, but 

 regularly rounded; hiatus long and narrow. 



Typical Species. 

 D. d a c t y 1 u s, Linn, (species.) 



Pholas dactylus, Linn. Syst. Nat. p. 1110. Linnaeus, Faun. Suec. 2124. 

 Anton, Verzeich der Conch, p. 1. Argenville, Concbyl. t. 3, f. k. m. 

 Barbut, Gen. Verm. t. 1, f. 11. Bonanni, pt. 2, f. 25, 26. Born, Test. 

 p. 14, t. 1, f. 7. Bosc, Hist. Nat. des Coq. ii. p. 194, t. 5, f. 1, 2, 3. 

 Brooke, Conch, t. 1, f. 7, 8. Brown, Must. Conch. Great Britain, p. 

 115, t. 49, f. 1, 2, 3. Bruguiere, Encyc. Meth. t. 168, f. 24. Catlow, 

 Conch. Nomenc. p. 3. Chemnitz, Conch. Cat. viii. t. 101, f. 857! 

 Chenu, Encyc. Hist. Nat. Moll. t. 33, f. 4, 5. DaCosta, Brit. Conch, p. 

 144, t. 16, f. 2. Deshayes, Encyc. Vers. iii. p. 753. Deshayes, Expl. 

 Sci. de l'Algerie Moll. p. 107, t. 9, C. E. & G. f. 13. (Animal.) Dill- 

 wyn, Desc. Cat. i. p. 35. Donovan, Brit. Shells, iv. t. 118. Favanne, 

 Conchyl. t. 60, f. al. Fleming, Edinburg Encyc. vii. p. 100. Fleming, 

 Brit. Anim. p. 457. Forbes and Hanley, Brit. Moll. i. p. 108, t. 3. Gi- 

 nanni, Op. post. t. 31, f. 184, 185. Gmelin, Syst. Nat. p. 3214. 

 Gualtieri, Test. t. 105, f. D. Hanley, Desc. Cat. p. 5. Herbst, Einl. i. 

 p. 115, t. 26, f. 1. Jay, Cat. 4th ed. p. 10. Jonston, De exang. t. 11, 

 f. 8, and t. 13. Karsten, Mus. Lesk. i. p. 150. Lamarck, Anim. sans 

 Vert. v. p. 444. Lamarck, (Desh. edit.) Anim. sans Vert. vi. p. 43. 

 Leach, Moll. Great Britain, p. 251. Lister, Conch, t. 433, f. 276. 

 Marvye, Meth. necess. aux Marins, t. 1, f. 10. Mawe, Conch, t. 3, f. 3. 

 Menke, Syn. Meth. p. 73. Montagu, Test. Brit. p. 20 and 528. Miiller, 

 Faun. Dann. p. 251. Murray, Fund. Testae, p. 40, t. 2, f. 3. Olivi. 

 Zool. Adriat. p. 93. Pennant, Brit. Zool. iv. p. 76, t. 39, f. 10. Petiver, 

 Gazoph. t. 79, f. 10. Philippi, Enum. Moll. Sicil. i. p. 3 and ii. p. 4. 

 Plancus, de Conch, p. 33. Poli, Test. utr. Sicil. i. t. 7, f. 111.. 

 Poiret, Voy. en Barbarie, nt. 2, p. 11. Potiez et Michaud, Gallerie des 

 Moll. ii. p. 268. Reaumur, Mem. de l'Acad. 1712, p. 125, t. 7, f. 1, 2.. 

 Reeve, Conch. Syst. t. 24. Reichenbach, Conchyl. p. 117, t. 725, 726.. 

 Roissy, Moll. vi. p. 438. Seba, Mus. iii. t. 16, f. 6 ab. Sowerbv, 



1862.] 



