BIVALVIA. 13 



Pecten clathrattjs, Roemer. Tab. I, fig. 19, 19a. 



Pecten clathratus, Roemer. Verst. Nordd. Oolith., t. 13, f. 9, 1836. 



• 



Testa ovato-orbiculari sub-cequivalvi, tenui plano-convexd ; auriculis magnis ineequali- 

 bus, valvd sinistra convexiord ; lineis radiantibus granulosis crebris incequalibus et irregu- 

 laribus, lineis concentricis obsoletis decussatis. Valvd dextrd lineis radiantibus remotioribus 

 et irregularibus, lineis concentricis clathrato-nodosis. 



Shell ovately orbicular, subasquivalve, thin, rather flattened, auricles very large, unequal, 

 and striated ; left valve moderately convex, with radiating densely arranged granulated 

 lines, irregular and unequal, crossed by very obscure closely arranged concentric lines, for 

 the most part obsolete. Right valve more flattened, radiating lines more remote, but 

 unequal and irregular, nodose where they are crossed by regular and distinct hnes consti- 

 tuting a finely cancellated surface. 



This very delicate and elegant species has the anterior auricles remarkably large ; the 

 right valve varies very considerably in the close arrangement of the radiating lines, and in 

 then prominence ; the concentric lines are very irregular, unequal, and uncertain in 

 their prominence, so that many specimens which appear shining and smooth to the 

 unassisted vision, disclose, under a magnifier, a very perfect and distinctly ornamented 

 surface. Its entire aspect is sufficiently characteristic to render it easily distinguishable 

 from contemporaneous species. 



Height, IS lines; lateral diameter, ]6 lines. 



Localities. Minchinhampton and Bisley Commons, in the shelly beds of the 

 formation. 



Hinnites, Be France, 1S31. 



Gen. Char. Shell ovate, sometimes oblique, irregular, inequivalve ; umbones de- 

 pressed, approximate ; auricles unequal, posterior auricle small, sometimes nearly obsolete, 

 anterior auricle produced ; left valve convex, right valve flattened, delicate, adherent. 

 Hinge straight without teeth, with a mesial trigonal fossa, as in Pecten. The surface is 

 ornamented with radiating, imbricated, or nodulated costae. 



There is usually some degree of obliquity in the valves; the convex valve is never 

 adherent, the other constantly so, which together with its extreme dehcacy will account for 

 it having been so rarely discovered. 



The shells of this genus have been described as Spondylus by Goldfuss, but they are 

 really very distinct from that genus ; the extreme delicacy and irregularity of the valves 

 would lead us to the distinction, irrespective of the hinge characters which are equally 

 distinct from those of Spondylus. 



The finest examples of this genus are found in the Inferior Oolite, both in number, 

 dimensions, and variety of ornament. 



