CAMAROPHORELLA 461 



mm., greatest width 16 mm., thickness 10.4 mm. The dimensions* of a 

 metatype of Seminula buckleyi are : length of pedicle valve 15 mm., length 

 of brachial valve 13.5 mm., greatest width 15.6 mm., thickness 7.9 mm. 



Pedicle valve deepest posterior to the middle, the umbo rather prom- 

 inent, the surface curving abruptly from the umbonal region to the 

 postero-lateral margins becoming distinctly inflected to the cardinal ex- 

 tremities, passing with a more gently convex curvature to the antero- 

 lateral and anterior margins ; mesial sinus originating at the beak where it 

 is narrow and shallow, growing distinctly broader and deeper towards 

 the front, rounded in the bottom, its sides curving regularly into the lat- 

 eral slopes of the valve ; the beak prominent and rather strongly incurved, 

 perforated by a foramen of moderate size which encroaches upon the um- 

 bonal region, the delthyrium closed by a pseudodeltidium above and by 

 the beak of the opposite valve below. Internally a strong median septum 

 extends anteriorly from the beak for nearly one-half the length of the 

 valve, the dental lamella? not clearly distinguished in any specimen ob- 

 served but probably joined to form a spondylium supported by the median 

 septum. 



Brachial valve about equally convex with the pedicle, its greatest depth 

 posterior to the middle, the surface sloping with a gently convex curva- 

 ture to the antero-lateral and anterior margins, curving somewhat more 

 abruptly to the postero-lateral margins, the beak strongly incurved and 

 passing beneath the margin of the pseudodeltidium of the opposite valve ; 

 a narrow, shallow, rounded, median sinus similar to, but somewhat smaller 

 than that of the opposite valve, originates at the beak and passes to about 

 the middle of the mature valve, where it gradually becomes obsolete, 

 mesial fold obsolete or slightly developed near the front margin in ma- 

 ture shells where it is scarcely differentiated from the general curvature 

 of the surface. Internally a strong median septum is present, extending 

 from the beak to about the middle of the valve, the remaining internal 

 features not observed. 



Surface of both valves marked by concentric lines of growth which are 

 variable in strength and distribution. 



Remarks. Only three examples of this rare species have come under 

 the observation of the writer, the largest being "Winchell 's holotype of the 

 species. The other two examples are from the collection of Prof. R. R. 

 Rowley, a cotype and a metatype of his Seminula ~buckleyi. The internal 

 features of the shell, so far as they are known, are shown only in the 

 larger of the two specimens from the Rowley collection. This specimen is 

 exfoliated sufficiently to clearly show the strong median septum in each 

 valve as a dark line passing anteriorly from the beak. The presence of 

 these median septa exclude the species from the group of athyroid shells 

 where it has usually been thought to belong, but without further knowl- 



