191 



third from the beak, marks the attachment of the adjuster muscle. 

 Opposite this there is a slight elevation or ridge on the median line. 



Sculpture. This consists of concentric ridges and lines, and of less 

 conspicuous radiating ridges. 



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

 one half of a millimetre shorter than the ventral valve. 



Horizon and locality. In a bed of fine gray shale, in the Dictyonema 

 beds, Div. 3 c., Navy island, St. John harbor, N.B. 



Although in some respect resembling a Lingulella, there are in others Resembles a 

 such wide differences in this little shell that we have sought for relations 

 in other genera, and notably to Obolella ". 



But as Obolella is now limited to thick calcareous shells, this species 

 cannot find a place there, and our later studies have induced us to look 

 to Hall's genus Leptobolus as the nearest approach to shells of this 

 type. 



The specimens from McLean brook, Cape Breton, are in better preserva- 

 tion than those of Navy island and show more clearly the characteristics 

 of the species, the description of which is here reported. 



Ventral valve. Interior. The cardinal area is from one sixth to one 

 quarter of the length of the valve. " The suboval scars " in the posterior 

 part of the shell are not now thought to be due to the adductor muscles 

 which are smaller and further forward. There is a narrow median 

 septum on some Cape Breton examples, extending from the umbo one 

 third of the length of the valve. There are also lateral ridges diverging 

 from the umbo ; and, extending in an arch from the anterior end of those 

 ridges, nearly parallel to the sides of the valve, are faint impressions of 

 vascular trunks. The " large bilobed sub-circular scar " is the area within 

 these trunks. 



Dorsal valve. Interior. There are faint impressions on the median 

 line in the anterior part of the valve that mark the position of the 

 anterior adductor muscles ; those impressions are about one-third from the 

 front of the valve. Extending back from this to the umbo is a sharp faintly 

 defined mesian' ridge. Lateral grooves or ridges extend out on each 

 side from the umbo nearly as far forward as the mesian ridge. 



Sculpture. The better examples from Cape Breton show that this 

 species had fine, well-marked concentric ridges ; the radiating ridges 

 belong to the surface of an inner layer of the shell. 



At the time this species was described, its affinities were obscure, be- 

 cause in such small shells, the details are not readily observed unless the 



