77 



is narrower in proportion to its length than the South American species, which 

 has about one-third of its posterior surface free from striae, while the striae in 

 the Campechensis are continued faintly over the entire posterior surface. 



Pholas oblongata, Say, has been entirely overlooked by European authors, 

 with the exception of Mr. Hanley, who has referred it doubtfully to D. da c- 

 ty 1 u s. It is figured in Tuomey and Holmes' Pleiocene Fossils of S. Carolina, 

 t. 24, f. 5. 



D'Orbigny's Pholas Candeana is a half-grown shell of this species. 



The only specimens that I have seen having the dorsal valves belongs to Mr. 

 Isaac Lea. They are identical in form with those of D. C h i 1 o e n s i s. 



D. Chiloensis, King, (sp.) 



Pholas Chiloensis, King, Zool. Journ. v. p. 334, 1832. Gay, Hist. Nat. 

 Chili, viii. p. 381. Sowerby, Monog. Pholas, Thes. Conch, ii. p. 486, 

 t. 102, f. 1, 2. Philippi, Neuer Conch, iii. t. 1, f. 4, 5. D'Orbigny. 

 Voy. p. 498. 



Dactylina Chiloensis, Chenu, Manuel, ii. f. 14, 15. 



Campechensis, (part.) Gray, Ann, and Mag. Nat. Hist. 2d ser. viii. p. 

 382. H. and A. Adams, Genera, ii. p. 326. 

 " Campechiensis, (part.) Fischer, Journ. Conch. 2d ser. iii. p. 49. 



Pholas laqueata, Sowerby, Proc. Zool. Soc. 1849. Sowerby, Monog. Pholas, 



Thes. Conch, ii. p. 486, t. 103, f. 19, 20. 

 Ilab.— Peru. Chili. 



Coll. Acad. Nat. Sci. Coll. Isaac Lea, LL.D. Coll. J. C. Jay, M. D. Coll. 

 G. W. Tryon, Jr. 



Pholas laqueata of Sowerby is a mere variety of Chiloensis, differing in 

 the greater prominence of the ribs and their arched scales. 



King, in his description, refers to Molina, Hist. Nat. Chili, p. 179, as authority 

 for the name ; but as it would be preposterous to allow such an obscure and 

 scant description as that of Molina's to remain as authority, I have thought it 

 best to use King's name in that connection. Gmelin (Syst. Nat. p. 3217) merely 

 copies Molina's description. 



Genus Monothyea, Tryon. 1862. 



Gen. Char. — Equivalve ; anterior hiatus long and narrow. Accessory plate 

 single, ovately triangular, with the base anterior and the nucleus subcentral. 

 Hinge processes cellular beneath. 



M. orien talis, Gmelin. (Species.) 



Pholas orien talis, Gmelin, Syst. Nat. 3216. Bosc, Hist. Nat. ii. p. 196. 



Bruguiere, Encyc. Meth. t. 168, f. 10. Catlow, Conch. Nomenc. p. 4. 



Chemnitz, Conch. Cab. viii. t. 101, f. 860. Dillwyn, Desc. Cat. p. 36. 



Hanley, Desc. Cat. p. 5, t. 2, f. 2. Jay. Cat. 4th ed. p. 10. Lamarck, 



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



vi. p. 44. Lister, Hist. Conch, t. 431, f. 247. Sowerby, Monog. 



Pholas, Thes. Conch, ii. p. 486, t. 102, f. 3, 4. Wood, Gen. Conch, t. 



14, f. 1, 2. Wood, Index Test. Pholas, t. 2, f. 1. 



Dactylina orien talis, Gray, Ann. and Mag. Nat. Hist. 2d ser. viii. p. 382. 

 H. and A. Adams, Genera, ii. p. 326. Chenu, Man. Conch, ii. f. 16. 

 Fischer, Journ. Conch. 2d ser. iii. p. 49. 

 Pholas Siamensis, Spengler. 



" dactylus, Solander MSS. teste Gray. 

 Hah. — India. 



Coll. Acad. Nat. Sci. Coll. Isaac Lea, LL.D. Coll. J. C. Jav, M. D. Coll. 

 G. W. Tryon, Jr. 



This species is placed by Sowerby, Gray and Chenu in the genus Dactylina. 

 although it is so very different in its single accessory valve. Sowerby's figure 



