142 



the latter which extend forward about one-third of the length of the valve 

 from the umbo, are sometimes nearly doubled in length, and extend along 

 the side of the depression marking the place of the central scars. Bet- 

 ween the central scars a distinct septum is found, which begins opposite 

 where the two inner pairs of ridges, described above, usually terminate, 

 though sometimes it may be traced as far back as the hinge area. Where 

 this ridge fades out in front is a depression, marking the place of the an- 

 terior lateral muscles. The central group of muscle scars extends to about 

 one-fifth from the front of the valve. The vascular trunks in this valve 

 are as far apart as half of the width of the valve. 



Sculpture. The general aspect of the surface ornamentation is describ- 

 ed in the earlier publication above cited, the following are further par- 

 ticulars. For the first two millimetres from the umbo the ridges are very 

 minute, or are absent; then outside of this they become visible with a 

 strong lens ; at from four to six millimetres from the umbo there are 

 about eight ridges in the space of a millimetre, and for the rest of the 

 shell about six to five, and finally four ; near the front of the valve the 

 ridges are lower, fainter and more closely set. The interior surface of 

 the valves in this species, often exhibit more or less irregular rows of 

 small pits ; the rows are in general concentric to the umbo, and give the 

 interior a rough appearance ; these rows are often found at the resting 

 stages in the growth of the shell, but other pits are miscellaneously dis- 

 tributed. 



Size as given above 15 x 17 mm.; depth of two valves about 4 mm. 



Horizon and locality. In assise E. 3d of the Upper Etcheminian at 

 Dugald brook, Escasonie; also at Gregwa brook, Escasonie, N. S. 



Except the following species. 0. lens, the Obolus nearest this age is (?) 

 major, of. the Upper Etcheminian in New Brunswick; that species, however, 

 is large, and does not have the concentric ridges, on the only example of it 

 which is known. None of the European Oboli have the sharp ridges 

 which mark the surface of this species, and they all belong higher in the 

 geological scale. Obolus (Michwitzia) monilifera, Linrs., has a flattened 

 dorsal valve, and thus differs from this species, it is also distinguished by 

 its beaded surface. 



This is the most noticeable brachiopod of the Upper Etcheminian 

 fauna, both for size and for the strong ornamentation of the valves. Like 

 Lingulepis Gregwa of the Lower Etcheminian fauna it seems to have 

 preferred a muddy bottom, as it is found to abound in the beds of Assise 

 d, which is more argillaceous than the assises above and below. 



