NEW FRESH WATER AND MARINE SHELLS. 279 



S. EBURNEA. PI. 39, fig. 1. — Oblong oval, equilateral, ventricose, thin; extremities nearly equally 

 rounded ; basal margin arched ; valves white, shining, minutely shagreened, towards the base minutely 

 rugose, with fine impressed radiating lines ; concentric lines towards the base finely waved, indenting 

 the margin. 



In this singular bivalve the pallial impression shows no junction with the adductor 

 impressions, but joins the extremities of the cardinal plate. The muscular 

 impressions are as distinct on the exterior as on the interior. 



PETRICOLA. 



P. siNuosA. PI. 39, fig. 2. — Subtriangular ; inflated anteriorly; profoundly sinuous posteriorly; ribs 

 radiating, prominent, acute, except towards the anterior margin, where they are replaced by closely- 

 arranged lines ; basal margin profoundly sinuous ; within brown, cavity of umbo white ■ cardinal teeth 

 prominent, two in one valve, and one broad one in the other. 



PHOLADOPSIS, Con. 



Inequivalved ; right valve produced posteriorly, left valve overlapping the opposite ; 

 cartilage situated on a projecting callus. 



P. rECTiNATA. PI. 39, fig. 3. — Ovate, very thin and fragile, profoundly gaping posteriorly ; profoundly 

 ventricose anteriorly ; valves with elevated waved laminae terminating near a profound sinus, which 

 extends from beak to base ; right valve undulated near the posterior end, reflected, margin pectinated ; 

 both valves have concentric lines. 



PARAPHOLAS, Con. 



P. BisuLCATA. PI. 39, fig. 4. — Ovate-oblong ; anterior accessory valves or deposit strong, shining, gibbous 

 on the margin of aperture, and having obscure decussated strice, the transverse ones a little raised ; 

 anterior side of the larger valves with numerous prominent crenulated radii ; a slightly oblique sulcus 

 extends from beak to base, and a slightly impressed line runs from the beak to the posterior end of the 

 closed portion of the base ; between the two impressed transverse lines the valves have closely- 

 arranged, rugose, longitudinal laminse, and posterior to these the laminae are remote and elevated. 



PENITELLA. 



p. WiLsoNii. PI. 39, fig. 5. — Ovate-oblong, very thin, profoundly ventricose ; valves with a furrow from 

 beak to base ; the papyraceous anterior valves very wide ; anterior valves with numerous oblique 

 waved laminae, and radiating acute ribs; ligament margin sinuous; posterior side with concentric 

 distant undulations; two small accessory valves behind the beak, which are reflected posteriorly; 

 membranaceous appendage with a sinuous or concave margin where it joins the shell, and a deep 

 annular groove anterior to the middle. 



This rare and beautiful shell is dedicated to that liberal patron of natural science. 

 Dr. Thomas B. Wilson, to whom we are indebted for a knowledge of the species. 



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