39 



Rhynchonella capax, Conrad^ sp. 



PL, Fig. 17 & 18. 



Rhynchonella capax (Conrad, sp.) , Meek, Keport Geol. Survey Ohio, 

 1873, I., Pt. 2, p. 123, t. 11, f. 6«/ 



Ohs. — A number of very beautiful external impressions, 

 often of the united valves, seem to me to be referable to 

 this species. They represent a rounded sub-globose form, 

 with close rather inrolled beaks, a well-marked fold and 

 and sinus, and numerous sub-angular costse, sometimes 

 very iine, crossed by innumerable decussating laminae. 

 The costae do not exceed twenty in number, but vary from 

 sixteen to twenty, seven to eight on the flanks, one to 

 three on the dorsal fold, seldom three, however, and only 

 one or two in the ventral sinus. The convexity of the 

 valves is about equal, and the fold relatively wider than 

 the sinus. The zigzag laminae increase rapidly in width 

 and prominence towards the front. 



In general habit, casts taken from these impressions are 

 very like Rhynchonella capax^ of the Hudson River Group 

 of iVorth America, and equally so of R. Lewisii, David- 

 son,^ from the Wenlock limestone of England, for indeed 

 the latter shells differ but little from one another. 



In R. capax the lateral costae are from four or five to 

 seven, on the dorsal fold four, and in the ventral sinus 

 three. In i?. Lewisii there are from two to five costae in 

 the fold, and one to four in the sinus. 



The Tasmanian impressions are certainly after the type 

 of these closely allied species, but apparently closer to R. 

 capax, in fact separated chiefly by the relative number of 

 costae. I therefore propose for our shell the varietal name 

 of meridionalis, and would write it in full as R. capax, 

 var. 7neridionalls, Eth. fil. 



Rhynchonella anticostiensis, Bilhngs," is also a close ally, 

 in fact Meek regards it as a synonym of R. capax. It 

 possesses four ribs on the fold and three in the sinus. 



In addition to the number of costae, the Tasmanian 

 shells differ only in being relatively smaller and less globose 

 than the American. 



Loc, — Heazlewood, in a blue-grey schistose rock. 



' Mon. Sil. Brachiopoda, 1869, Pt. 7, No. 3. p. 180, t. 23, f. 25-28. 

 2 Pal. ¥o&s. Canada, 1862, I., Pt. 3, p. 142, f. 119a-c. 



