67 MOLLUSCA OF THE GuLF OF MEXICO 35 



(Gregarie!!a) opifex 



Modiola opifex Saj^, Jour. Acad. Nat. Sci. Phila., 4, p. 369, 

 pi. 19, f. 2, a-b, 1825 ; Philippi, Abbild. u. Beschr. n. 

 Conch., 3, Modiola, p. 21, t. 2, f, i ; Dall, B. M. C. Z., 

 12, p. 235, '86 ; Bull. 37, U. S. N. M., p. 38, '89 ; Check- 

 list N. W. Coast, p. 18, 19 16. Botulina Dall, synonym of 

 Gregariella Monterosato . 

 Distribution. — Hatteras to Brazil (Kroyer), 0-52 fms. Also 

 Californian coast. Gulf of Mexico, Yucatan Strait, 640 

 fathoms, (accidental, Dall). This verj^ beautiful species 

 weaves nests of byssal silk. 

 (Brachydontes) demissus Dillwyn, Cat. Rec. Shells, i, p. 314, 

 1817 ; Say, Jour. Acad. Nat. Sci. Phila., 2, p. 265, 1822. 



Modiola plicatula Lamarck, An. s. Vert., 6, p. 113, 1819 ; 

 DeKay, Nat. Hist. N. Y., Moll., p. 184, pi. 24, f. 258, 

 1843 ; Verrill, Inv. Vineyard Sound, p. 693, pi. 31, f. 238, 

 '73 ; Dall, Bull. 37, U. S. N. M., p. 38, pi. 54- f- i, '89 : 

 Singley, Fourth Ann. Rept. Texas Geol. Surv., p. 325, '92. 



semicostatus Conrad, Jour. Acad. Nat. Sci. Phila,, 7, p. 244, 

 pi. 20. fig. 7, 1837. Not Dall, Bull. 37, '89. 



demissusN-a.n2i\X'3i, Pioc. Acad. Nat. Sci. Phila., vol. 55, p. 

 756, 1903 ; Dall, in Matson, U. S. G. S. Prof. Paper, 98- 

 L, p. 177, 1916. 

 Distribution. — Nova Scotia to Texas. Pliocene to Recent. 

 Gulf coast-— Cedar Keys, St. Marks, Fla. ; Belle Isle, 

 Week's Island, Chandeleurs,'La. ; Lavaca, Matagorda and 

 Galveston bays, Texas. Pleistocene : New Orleans pump- 

 ing station No. 7 ; North Creek, Fla. ; Ft. Morgan well, 

 Ala. at 217-321 feet. Pliocene : Caloosahatchie. 

 Remarks. — Abundant in the streams of salt marshes imbedded 

 in the peaty soil of the banks as at Week's Island, forming 

 sod-like masses among the sedges and grasses. Mitchell 

 has proved by experiments that this species can live 

 twent3'-two days without water. 

 (Brachydontes) citrinus Bolten. 



Mytilus citrinus Bolten, Mus. Bolt., p. 157, 1798. 



