Maryland Geological Survey 407 



impressed ; aperture rather narrow, outer lip strongly varicose, the varix 

 produced backward upon the penultima ; outer base of varix marked by a 

 series of shallow, parallel sulcations, ten or twelve in number, the relics 

 of the impressed spiral sculpture; inner lip probably heavily calloused, 

 bearing at the base two prominent oblique plications, and, half-way between 

 them and the posterior commissure, a less prominnent horizontal fold; 

 base emarginate. 



Dimensions. — Altitude 12.6 mm., maximum diameter 10.7 mm. 



Type Locality. — Two miles southwest of Oxon Hill, Prince George's 

 County. 



This species differs from the preceding in the lesser number of spiral 

 lirations and the greater angularity. Avellana costata (Johnson) is much 

 smaller and more slender, both absolutely and relatively. 



Occurrence. — Monmouth Formation. Brightseat, and 2 miles south- 

 west of Oxon Hill, Prince George's County. 



Collection. — Maryland Geological Survey. 



Family AKERATIDAE 



Genus HAMINEA Gray 

 [Am. Mag. Nat. Hist., vol. xx, 1847, p. 268] 



Type. — Bulla hydatis Linne. 



Shell very thin, inflated, oval or subcylindrical in outline; spire invo- 

 lute. External surface finely striated. Aperture as long as the shell, 

 narrow posteriorly, broader and somewhat patulous in front. Outer lip 

 thin, sharp, nearly vertical in the medial portion. Columella thin, not 

 glazed or plicate. 



Haminea has been an inconspicuous element in the molluscan faunas 

 from the Cretaceous to the Recent. 



A. Body whorl medially inflated, basally constricted Haminea mortnni 



B. Body whorl cylindrical in outline Haminea cylindrica 



Etymology: Hamus, a hook. A name suggested by the outline of the 

 aperture. 



