NATURAL SCIENCES OF PHILADELPHIA. 4G3 



Dimensions. Length (of valves) 5-20ths, breadth 4-20ths. The embryon- 

 ic state of some of the specimens which occur living in cork, as well as the na- 

 ture of the material, induce me to consider this species indigenous. The pos- 

 terior auricle is so small in comparison with that of T. megotara, that Dr. 

 Lukis proposed the name of " microtara" for this species. Specimens in cork 

 are frequently encysted. Jeffreys. 



h. External surface of the valves ornamented by a narrow radiating area with 



crowded scidptured lines. 



* Pallets. 



Blade spatulate, truncate at the end. Concave on one ).Norvaeica 



side, convex on the other. Tube concarnerated. j 



Blade spatulate, truncate at the end. Concave ou one ^g^,. 



side, convex on the other Tube ? } 



Blade spatulate, truncate at the end. Concave on one )d'var"catn 



side, blade very short. Tube concarnerated, J 



Blade spatulate, but the sides incurved in the middle, l nava i; g . 



end margin concave. Tube not concarnerated, J 

 Somewhat hastate, but truncate and heart-shaped at)megotara 



the end. Tube not concarnerated y nana. 



Angularly ovate, dilating into a broad blade, abruptly ),j;i a + a + a 



truncate. Tube not concarnerated J 



Transverse, end margin sinuous, stalk deflected at ani 



angle from the plane of the blade. Tube not con- ^malleolus. 



camerated y 



Palseform, dilated, profoundly emarginate at the end. ) , . 



Tube? j-eiongata. 



Obliquely truncate, tridentate and serrate at the end. ) . . 



Tube? j-truncata. 



Narrow, long, colored, stalk white. Tube not concam- ) , . 11oto 

 erated ' p eaice 1 lat a . 



* * Valves. 



Posterior auricle broad, towering above the beaks, its'} m e + a 



basal edge situated lower than that of the anterior V 



4 nam a. 

 area y 



Posterior auricle broad, not extending above the beaks, ^navalis 



its basal edge situated lower than that of the ante- Vpedicellata 



rior area jdilatata. 



Posterior auricle broad, not extending above the beaks, ) ^ 



its basal edge even with that of the anterior area ) ' l " 



Posterior auricle narrow, apex extending above the l 



beaks, the lower edge even with that of the ante- [-malleolus. 



rior area J 



Posterior auricle narrow, apex not extending above the } 



beaks, the lower edge even with that of the ante- >divaricata. 



rior area y 



The above table of distinctive characters must be used with extreme cau- 

 tion, as individuals of the various species sometimes occur which do not well 

 accord with their characters as given therein. 



Several East Indian species are but partially included, because the descrip- 

 tions are not sufficiently accurate for the arrangement of their valves. 



T. elongata, Quatrefages. 



T. elongata, Quatrefages, Ann. Sc. Nat. 3d ser. xi. p. 33. Adams, Genera, 



ii. p. 333. Fischer, Journ. de Conchyl. 2d ser. i. p. 133. Jeffreys, 



Ann. and Mag. Nat. Hist. 3d ser. vi. p. 126. 

 T. Senegal ensis, Fischer, Mel. Conchyl. p. 19, t. 4, f. 26. 



1862.] 



