40 



Rhynchonella borealis, Schlotheim ? 



PI., Fig. 19 & 20. 



Rhynchonella borealis (Sclil.), Davidson, Mon. Brit. Sil. Brachio- 



poda, 1869, Pt. 7, No. 3, p. 174, t. 21, f. 14-20. 



Obs. — Numerous examples of a crushed Rhynchonella 

 have yielded characters that place it very near to the 

 above species, particularly one variety figured by Davidson 

 (.swhis. t. 21,f. 18, 18a.) 



I believe the fossils are the remains of a subtrigonal 

 shell, with the fold of the dorsal valve abruptly raised, with 

 wide smooth sides, and the crown of the fold longitudinally 

 and narrowly sulcate, the single rib or costa thus formed 

 on each side being sharp and well defined. The flanking 

 costae, from three to four in number, are also prominent 

 and sharp. The sinus of the ventral valve is wide and 

 deep, with two insignificant costee at the bottom close 

 together. There are four costse on each flank, and the 

 intercostal spaces or valleys on both valves are deep. The 

 whole surface of the valves is crossed by wery strong con- 

 centric frills. 



Our fossils are not only closely allied to the form of R. 

 borealis, already indicated, but also to its variety diodonta, 

 Dalman, and they have some characters in common with 

 R. bidentata, Hisinger,^ and R. altiplicata, Hall,^ of the 

 Lower Helderberg Group of North America, but, as re- 

 gards the former of these, not possessing so high a dorsal 

 fold, and more costae. 



Loc. — Zeehan, in a greyish-white schist. 



Genus Strophomena, Rafinesque. 



Strophomena ? sp. ind. 

 PL, Fig. 12. 



Obs. — An impression of a very peculiar Strophomenoid 

 shell that is worth figuring to draw attention to it, although 

 of doubtful generic identity. There is evidence of a large 

 sinus, thereby indicating a ventral valve. The sinus is too 

 pronounced for the specimen to be a species of Orthis^ 

 except such species as O. biforata, Schlotheim, of the 

 Middle and Upper Silurian, but it is unlike the latter in 

 outline. So far as mere shape is concerned it approaches 

 Tropidoleptus, Hall, or Enteletes, Fisher. 



Loc. — Zeehan. 



1 Davidson, loc. cit., 1883, V., Pt. 2, p. 150, t. 10, f. 3, a $• b. 



2 Pal. N. York, 1852, II., p. 231, Atlas, t. 33, f. 2 a-n. 



