FAUNA OF THE ST. JOHN GEOUP. 49 



Var. lyncioides. (PI. XII, figs. 10 a-c) 



Distingnishod by its sharp, strong, radiatiug ribs, large umbo and high cardinal area, 

 lu some of the larger examples the radiatiug ribs become subordinate to and are replaced 

 on the newer part of the shell by concentric strite, reversing the usual position of the 

 ribbed and the smooth parts of the shells of this species. &ize of the valves about 

 6x8 mm. 



Var. slrophomenoides. (PI. XII, figs. 12 a and b.) 



This form shows very few radiating strise, except on the dorsal valves, on which they 

 are faintly shown. The valves are concentrically wrinkled like those of Stropliomena 

 rhomboidalit, but not in so di.stinct a manner. The ventral valve is abruptly bent down 

 on the sides and front about one-third from the outer margin ; this valve when young is 

 flat and the umbo is more pointed than at a later stage of growth Size, 4'5 x G'ô mm., 

 and 5' x 65 mm. for the dorsal and ventral valves respectively. 



These abberrant forms of O. lenticularis possess considerable interest in connection 

 with the question of the development of new genera from older types of brachioiJods. 

 Not that an Atrypa, a Platystrophia or a Strophomeua necessarily sprung from this 

 species, but they show the power of the Orthid type to develop such genera and sub- 

 genera. 



Mr Billings described a Strophomena (S. aurora) from a band immediately below the 

 beds with Phyllograptus in Newfoundland, and Dr. Brogger'a variety of .S. rhomboidalis as 

 low down as the Asaphus expansus shale in Norwai»^, or close to the base of the Ordovician 

 system. 



OETHISINA, aOrbignu. 



OrTHISINA (?) JOHANNENSIS, n. sp. (PI XII, figs. 13 a-c). 



Shell subquadrate, doubly convex, rather flat, very thin. 



Dorsal valve depressed at the sides and front, and having a broad, shallow median 

 sinus. The valve is about one-quarter wider than long, and the hinge-line is nearly as 

 long as the length of the shell. Umbo slightly elevated, hinge-plate weak and thin. 



Yentral valve depressed at the sides, and having a few median ridges running from 

 the umbo to the front of the shell. This valve is somewhat geniculated at two-fifths of 

 its length from the umbo, and from the bend faintly raised ridges diverge to the anterior 

 angles of the shell ; behind the geniculation the surface of the shell is marked by faint 

 undulations similar to those of Strophomena rhomboidalis. 



The umbo is not prominent, but the back of the valve is regularly curved and the 

 area rather low. 



Sculpture. — Closely set striae radiatiug from the umbo, and faint concentric striae mark 

 the shell. 



Size. — Length of the ventral valve, 9 mm. ; width, 10 mm. Length of dorsal, 8 mm. ; 

 width, 10 mm. 



Horizon and Locality. — Limestone lentiles in the black shales of Division 3 a, Germaine 

 street, St. John. 



Sec. IV, 1891. 7. 



