6 7 



MOIXUSCA OF THE GULF OF MEXICO 



35 



(Gregariella) opifex 



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

 pi. 19, f. 2, a-b, 1825 ; Philippi, Abbild. u. Beschr. 11. 

 Conch., 3, Modiola, p. 21, t. 2, f, 1 ; 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 very beautiful species 

 weaves nests of byssal silk. 

 (Brachydontes) demissus Dillwyn, Cat. Rec. Shells, 1, 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. 1, '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. 



demissus Vanatta, 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,'L a - ; 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 

 twenty- two days without water. 

 (Brachydontes) cltrinus Bolten. 



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



