FOSSILS. 599 



valve moderately convex, carinate in the middle by a strong plication 

 with six or seven smaller ones on each side, the lateral ones slightly 

 curved towards the outer extremity. Dorsal valve concave, with 

 a broad shallow mesial sinus, the margins on either side being bent 

 a little upward, giving a sinuous outline to the margin of the shell ; 

 surface marked by fine concentric strias. 



This species resembles the L. hemispherica of the Clinton group 

 in New York in general form, but the hinge-line is shorter, and 

 the extremities rounded ; the mesial elevation consists of a single 

 strong plication, while in L. hemispherica the surface is regularly 

 plicated, with the central one sometimes a little stronger than the 

 others. Arisaig, coll. J. W. D. 



Atrypa reticulains, Dalman, Arisaig. East River, coll. J. W. D. 



Atrypa emacerata, Hall. Arisaig, coll. J. W. D. 



Athyris [Merista) didpna, Dalman. East River, coll. J. AV. D. 



Orthis testudinaria^ Dalman. Arisaig, coll. J. W. D. 



Lingula oblonga, Hall. Arisaig, coll. J. W. D. 



Lingula, (?) n. s. Mcrigomish, Dr Honcyman. 



Modiolopsis (?) rhomhoidea^ Hall (Fig. 203). Shell sub^rhomboid, 

 rounded in front, wider and obliquely truncate behind, hinge-line 

 slightly ascending from the anterior end ; beaks subterminal, posterior 

 umbonial slope obtusely subangular below, anterior to which the 

 shell is flattened ; basal margin nearly straight, the shell gradually 

 widening behind, and the posterior basal extremity abruptly rounded. 

 Surface evenly striated concentrically. 



Anterior muscular impression very strong, posterior muscular im- 

 pression less strongly defined, but still very conspicuous and sub' 

 duplicate ; palleal line simple, nearly parallel to the basal margin, 

 strongly and almost equally defined in all parts of its length between 

 the two muscular imprints. 



This shell bears some resemblance to M. primigcnius, but is less 

 vcntricose in the middle, and the sub-angular umbonial slope is not 

 so well defined in that species. Arisaig, coll. J. W. D. 



Modiolopsis suh-nasidus, Hall. Shell elongate sub-spatulate, the 

 length being more than twice the greatest width at the hinge-line ; 

 slightly ascending posteriorly ; beaks sub^anterior, the anterior end very 

 narrow, gibbous on the umboncs, with a sub-angular ridge on the 

 umbonial slope which extends to the postero-basal angle ; basal 

 margin nearly straight, the posterior end somewhat flattened and 

 obliquely sub-truncate at the extremity ; surface marked by con- 

 centric lines of growth. 



This shell bears a close general resemblance to M. nasidus of 



