MARYLAND GEOLOGICAL SURVEY 203 



Order PRIODRSMACEA. 



Superfamily MYTILACEA. 

 Family MYT1LIDAE. 



Genus MYTILUS Bolten. 

 Section HORMOMYA Morch. 



Mytilus hamatus Say. 

 Plate LX, Figs. 5, 6. 



Mytilus hamatus Say, 1822, Jour. Acad. Nat. Sci. Phila., vol. ii, 1st ser., 



p. 265. 

 Mytilus hamatus Dall, 1889, Bull. U. S. Nat. Mus., No. 37, p. 38. 

 Mytilus (Hormomya) hamatus Dall, 1898, Trans. Wagner Free Inst. Sci., 



vol. iii, pt. iv, p. 789. 



Description. — " Shell very much contracted and incurved at the base, 

 which is acute; valves striated on every part of the exterior with longi- 

 tudinal, elevated lines, which are bifid and sometimes trifid towards the 

 tip; color dark fuscous; within dark purpurescent, with a whitish mar- 

 gin." Say, 1822. 



The earliest occurrence of this species is in the Pliocene of Florida. 

 It has been found in the Pleistocene of Massachusetts and Maryland and 

 in the Eecent ranges from Long Island southward to Costa Pica. 



Width, 20 mm. ; height, 33 mm. 



Occurrence. — Talbot Foemation. Wailes Bluff near Cornfield Har- 

 bor, St. Mary's County. 



Collections.- — Maryland Geological Survey, Johns Hopkins University, 

 and IT. S. National Museum. 



Superfamily NAIADACEA. 

 Family UNIONIDAE. 



Genus UN 10 Retzius. 



TJnio complakatus (Solander) Dillwyn. 



Plate LX, Figs. 7-11. 



Mya complanata Solander, No. date, Ms. in the British Museum. 



Mya complanata Dillwyn, 1817, Cat. I, p. 51. 



Vnio complanatus Simpson, 1900, Proc. U. S. Nat. Mus., vol. xxii, pp. 720-725. 



