

192. 



mud in which they were preserved was very fine and had escaped altera- 

 Reasons for *i n - This was not altogether the case at Navy island in St. John basing 

 t k u * ^ ne me dium of preservation at McLeod brook is in a more satisfac- 

 tory condition, and hence we were able to see more readily points of 

 resemblance to the genus Leptobolus. 



In Obolella the shell substance is calcareous and thick ; in this there 

 is a chitineous film, and the shell is quite thin. No very satisfactory 

 impressions of vascular trunks were observed, but the position of the 

 muscle scars and of the median ridge in both valves are most in accord 

 with Leptobolus. 



From Lingulella this species is distinct by the uniform thickness 

 and tenuous substance of the valves. In Lingulella there is a 

 thickening, of the shell in the visceral cavity, while around the brachial 

 cavity it is -usually much thinner; in Leptobolus the shell-substance is~ 

 thin and comparatively uniform except at the cardinal area of the 

 ventral valve. 



In the paragraph of the original description of this species, " In the 

 general form," &c., the features described resemble the characters of 

 Leptobolus as much as Obolella. or more so. 



Size. Length of ventral 4 mm.; width 3J mm. The dorsal valve is 

 one-half millimetre shorter. 



Horizon and locality. Fine dark gray shale of Div. 3 c. at McLeod 

 brook, Cape Breton, N.'S. 



By comparing the figures of the Navy island form with these, it may 

 be gathered that the posterior cavity (scar) or depression of the ventral 

 valve occupies the space of the visceral cavity, while the anterior depres- 

 sion is outlined by the vascular trunks. The ridge between these two de- 

 pressions in the Navy island form might be compared to the cross-ridge 

 in the shell of Leptobolus which Prof. Hall seemed to regard as of 

 generic value. 



LEPTOBOLUS, cf. LINGULOIDES. 



Leptobolus cf. A small linguloid shell is not rare in the fine shale of McLeod brook. 

 es ' As in others of this genus, the umbo of the ventral is weak and short, 

 and so the two valves are hot easily distinguishable. Owing to the thin- 

 ness of the valves the internal features are only faintly indicated. The 

 ventral shows two lateral ridges diverging from the umbo, and a callus is 

 obscurely indicated ; one example shows a trace of a vascular trunk on 

 one. side. The dorsal has an obscure medium septum extending to the 

 middle of the valve. 



