102 G. F. MATTHEW ON THE 



Size. Length 22 mm., width 27 mm. 



Horizon and Locality. — Same as the preceding. 



This species is the hirgest Orthis known from the St. John Group. It is from the 

 same horizon as the English species cited ahove, and resembles it in form, but the ribs are 

 twice as numerous and the shell much larger. Until better known it may be placed here. 



There are several American species which approach it in size. Orlhis C/ijlie, Hall, of 

 the Trenton has similarly numerous ribs and an oblately rounded form, but there appears 

 to be no Chazy or Calciferous species like it ; it has a more rounded form than either O. 

 imperator or O. plali/s, Bill., of the Chazy ; it agrees in form with 0. porcata, McCoy, (Tren- 

 ton to Clinton) but has twice as many ribs ; it has about the same number of striae as O. 

 ainnata, Hall, of the Hudson R. shales, but the hinge-line is shorter, aud from O. occidentals. 

 Hall, of the same terrane it differs by its more numerous ribs and rounder form. 



Oethis Carausii, Salt. ? (PI VII., iigs. T a and h) 

 Geol- Mag. vol. v., p. 315. PI. xvi., tigs. 23 a and c. 



A small species from the lower part of the Bretonian Division (Div. 3) appears to 

 agree with the above species, which Davidson has figured and described. It has about a 

 dozen low, rounded ribs, a broad umbo and a low hinge area. 



Size. Length 7 mm., width 10 mm. 



Horizon and Locality. In fine dark shales of Div. 3« at Navy Island, scarce. 



A variety (perhaps of this species) with more numerous ribs (about 20) but of about 

 the same size is found higher up, in the lower Dictyouema slates (Div. 36), at the same 

 locality. 



STEOPHOMENA, Blainv. 



Strophomena ATA va n. sp. (PI. VII., tigs. 8 a — f.) 



Nat. Hist. Soc. of N.B., Bulletin x., p. vii. 



Narrowly semicircular. Valves slightly arched, rather wider than the hinge-line, 

 compressed at the cardinal angles ; sides of the valves nearly straight behind, regularly 

 rounded in front. 



Ventral valve moderately convex, highest and somewhat angulated at the middle of 

 its length : umbo inconspicuous aud appressed to the very narrow area. 



Doi'sal valve somewhat concave especially toward the umbo, which is depressed to 

 the general level of the valve. 



The interior of the ventral valve has characters intermediate between those of Orthis 

 and Strophomena. The ridge inclosing the cardinal muscles are shorter and closer at 

 their extremities than in Strophomena, aud the scar of the adductor muscle is broader 

 and shorter, but extends half way to the front of the valve. There is a low sharp ridge at 

 the umbo between the branches of the posterior cardinal muscle, and the ventral cavity is 

 faintly outlined in front. Another cast of the ventral valve of a larger individital, per- 

 haps of this species, shows the impressions of the muscles more distinctly ; in this the 

 impression of the adductor muscle is much nearer to the hinge, being about two-thirds 

 from the front of the valve : there is a low callus in front of the imprint of the adductor 

 muscle. 



