NATURAL SCIENCES OF PHILADELPHIA. 469 



Hah. England ; Holland ; Senegal ; United States ; North. Sea ; Mediterranean 

 Sea. 



Coll. Acad. Nat. Sc. Helgate, New York, from a British frigate sunk dur- 

 ing the revolutionary war. 



Description. Valves about equal in length and breadth, much resembling 

 in general form those of T. Norvagica, but with the posterior auricle 

 expanded somewhat laterally, and its base extending lower than that of the 

 anterior area. The anterior area moderate, not generally so large in propor- 

 tion to the valve as that of Norvagica, and having a more convex basal 

 margin ; it inclines somewhat obliquely downwards to the fang, its junction 

 being considerably higher up than that of the posterior auricle. Anterior 

 lateral margin of the fang nearly straight ; posterior lateral margin much 

 shorter than the other, on account of the lower extension of its auricle, very 

 oblique. Fang acuminating rapidly towards the base. Posterior auricle not 

 ascending, but produced laterally, its dorsal edge mostly somewhat concave, 

 lateral margin nearly straight, a little oblique, rounded at each end. Basal 

 margin slightly declining towards the fang, shorter than the dorsal edge on 

 account of the expansion of the fang laterally. 



The internal ventral tubercle and the dorsal rim do not differ from those of 

 T. Norvagica. The apophysis is broad but thin, not thickened at the 

 end, and the same breadth throughout ; it is twisted so that oue sharp edge, 

 instead of the flat of the blade, is turned towards the interior surface of the 

 fang. The posterior auricle is defined by a close, projecting rim. 



Externally, the anterior area is closely striated concentrically, and its pos- 

 terior limit is defined by an impressed line ; succeeding to this is a radiating, 

 narrow area, the closely decussated stripe of which, are sometimes quite prom- 

 inent ; posteriorly the surface is slightly striate concentrically, becoming 

 smooth. The auricle is defined by a sudden depression in the level of the 

 surface of the fang. 



The pallet is convex on one side and plane on the other ; the stalk, which 

 is about as long as the blade, is moderately thick, and flexuous ; it is not con- 

 tinued as a rib beyond the commencement of the blade, which differs from 

 that of T. Nor vagi c a by being more convex below, (the entire base being 

 semi-circular) with the sides concave, and the end two-pointed, caused by a 

 decided concavity of the centre of the margin. Tube not concamerated, long, 

 flexuous, solid, polished, gradually narrowing. 



Valves and pallets each one-fourth of an inch, and the tube eight inches in 

 length. 



This species is the T. m a r in a of Sellius, who published, in 1733, an excel- 

 lent description and figures. Unfortunately his name cannot be adopted, be- 

 cause pre-Linurean, and this is the more to be regretted since the description 

 in the Syst. Nat.* will apply to any species in the genus, and the speoies is 

 only limited by the reference to the figures of Sellius. 



Mr. Hanley, as one important result of his laborious examination of the types 

 in the collection of the great Swedish naturalist, demonstrated its identity 

 with the species of Sellius. 



The navalis of Brit: authors prior to Forbes and Hanley, is T. Norvagica, 

 Spengler. Many of the authorities quoted above must be admitted with doubt, 

 several of their descriptions are equally applicable to any species, and occa- 

 sionally the figures are no more characteristic! 



It is doubtful whether the navalis of Sicily, Corsica and the Black Sea is 



* " T. Testa tenuissiina cylindrica leevii." Linn. 



f The synonymy and specific description in Deshayes' Expl. Srientifique de 1'Algerie, Mollus- 

 queg, must be taken wilh great caution. The fast is an indiscriminate grouping of references to 

 all the species described by different authors, as the T. navalis of Linn., and the lust is sufficiently 

 general to cover them all ! 



1S62.] 



