30 



In the interior of the ventral valve the muscular space is sub-triangular, 

 rounded in front, with straight or gently concave sides, and extends about 

 half the length of the shell. The width of this space, in a specimen thirty 

 lines wide on the hinge line, is thirteen lines across the anterior angles. Its 

 length the same (fig. 6a.) In a smaller specimen, sixteen lines wide on 

 the hinge line, the length of the space is about seven lines, its width at the 

 front five lines, (fig. 6.) The divaricators are divided into a number of 

 longitudinal lobes, seven or eight in large individuals, fewer in the smaller, 

 and sometimes very indistinct. The occlusors are narrow and half the 

 ength of the other two, very indistinct. The mesial septum sometimes 

 extends the whole length of the muscular impressions, and becomes stronger 

 on approaching the beak ; in the small specimens it is very slight or absent 

 altogether. 



Surface with fine, rounded radiating striae, ten or twelve in the width 

 of two lines. These are crossed by very fine concentric strise, which dis 

 appear when the shell is slightly worn or exfoliated. In the cast of the 

 inner surface of the ventral valve, all the space between the muscular 

 impression and the cardinal angles is punctured. All around the sides 

 and front margin the punctures are very small, and partially arranged in 

 rows conforming to the radiating striae. 



.The specimens as yet collected are not in a condition to show the area 

 perfectly. It is, however, vertically striated and denticulated throughout 

 nearly, if not entirely, the whole length. There seems to be a small trian- 

 gular deltidium with a cavity beneath it. 



Width of the largest specimen collected forty-two lines ; length of the 

 same three inches ; dorsal valve unknown. 



In S. Blainvillei the divaricators extend nearly two-thirds the length of 

 the shell ; in this species about half the length. It approaches S. magnifica 

 in size, but the form and proportional length of the muscular impressions 

 are different in the two species. It is closely related to S. Beckii, Hall, 

 but attains a much larger size ; is not concentrically wrinkled ; has finer 

 radiating striae and a deltidium. Sir ene has only four or five radii in 

 the width of two lines while this species has ten or twelve. 



Locality and Formation. — Mount Joli and Split Rock, Perc^. Lower 

 Devonian. 



Collectors. — Sir W. E. Logan, Thomas Curry. 



Strophomena punctulifera, (Conrad). 



Plate 3, fig. 2. 



Strophomena punctulifera, (Conrad.) Ann. Rep. Pal., N. Y., 1838, p. 117. 

 Strophomena punctulifera, (Vanuxem.) Geol. Rep. 3rd Dist, N. Y., 1843, p. 122. 

 Strophomena euglyphAj (Conrad.) Ann. Rep. Pal., N. Y., 1841, p. 36. 



