548 Systematic Paleontology 



species from a fragment of a valve. The fragment in question, however, 

 suggests I. confertim-annulatus Eoemer more strongly than any other 

 species, although it is apparently less inflated. 



Occurrence. — Monmouth Formation. Brightseat, Prince George's 

 County. 



Collections. — Maryland Geological Survey. Xew Jersey Geological Sur- 

 very, U. S. National Museum. 



Outside Distribution. — Monmouth Formation. Navesink marl, New 

 Jersey. Austin Chalk. Texas. 



Family PTERIIDAE 



Genus PTERIA Scopoli 



[Introd. ad Historiam Naturalem, 1777, p. 397] 



Type. — Mytilus hirundo Linne. 



Shell inequivalve, inequilateral, auriculate, anterior ear comparatively 

 small, posterior aliform ; byssal sinus under anterior auricle of right valve ; 

 exterior surface almost smooth, lamellar or striated, interior nacreous; 

 umbones low but sharp; hinge line elongated, straight, a single cardinal 

 tooth placed under the umbone of each valve, often supplemented by a 

 laminar lateral tooth ; ligament marginal, partially internal, partially 

 external ; pallial line entire ; adductor impression subcentral. 



The genus has a vast stratigraphic range, from the the Silurian onward. 

 The recent species number about one hundred and twenty, and are limited 

 for the most part to tropical and subtropical waters. Among them may 

 be mentioned the Antillean pearl oyster, Pteria radiata Leach. 



A. Base line arcuate, not approximately parallel to the dorsal margin. 



Pteria petrosa 



B. Base line straight, approximately parallel to the dorsal margin. 



Pteria rhombica 



Pteria petrosa (Conrad) Meek 

 Plate XXI, Fig. 10 



Avicula petrosa Conrad, 1853, Jour. Acad. Nat. Sci., Phila., 2d ser., vol. ii, 



p. 274, pi. xxiv, fig. 15. 

 Avicula lingucrformis Evans and Shumard, 1854, Proc. Acad. Nat. Sci., 



Phila., p. 163. 



Etymology: -mipov, wing. 



