136 



laterals are far advanced to the front and are placed close together ; in 

 Lingulella the anterior adductors are also about the mid length of the 

 valve, while the " j " laterals, approximated as in Obolus, are a little in 

 front of these adductors; in Eoobolus a third relation between thesemuscle 

 pits is found ; the group of muscles as a whole was in front of the centre of 

 the valve, but the two pairs of muscles were almost or quite in line, longi- 

 tudinally, with each other, and are arranged more or less in a quadrate 

 manner. Beside these four pits of the central group, usual in the Lingu- 

 loid Brachiopods, there is in this genus a fifth, being a small single scar 

 on the axial line, sometimes equidistant from the other four and sometimes 

 a little in front of the " j " laterals. This pit appears to mark a small 

 muscle whose office is unknown. 



The arrangment of the vascular trunks in this subgenus, so far as 

 known, is similar to that in Obolus and Lingulella. This subgenus, 

 Eoobolus, characterizes the Lower Etcheminian Fauna. 



OBOLUS TRIPARILIS n. sp. Pi. VIII, fig. 4 a c and PI. IX, figs. 1 a and b. 



A lenticular, rather thick shelled species, the inside of the shell showing 



Obolus (E.) concentric rows of perforations like Lingulella Davisil. 

 tnparihs 



Ventral valve longer than wide, decidedly pointed behind, the part of 

 the valve in front of the umbo, rather prominently raised and the 

 slopes on each side depressed ; valve somewhat flattened in front, else- 

 where evenly arched. Interior not known, but there are indications 

 that the callus extended as far as the middle of the valve. 



Dorsal valve about as long as wide, somewhat flattened along the 

 median line. Interior. A broad striated hinge-area lies across the car- 

 dinal end of the valve and runs forward on the lateral margins. Along 

 the middle of the valve runs a long, raised callus, extending in some 

 examples to within a quarter of the front of the valve, in others, less ; 

 this callus is about one fifth of the width of the valve ; it is traversed 

 lengthwise by a median and two lateral septa, of which the latter branch 

 near the front, each branch, and the median septum extending respectively 

 to three small muscle scars. Of the central group of muscle scars the two 

 posterior are larger than the others which are of nearly equal size, and some- 

 times nearly equally advanced toward the front of the valve. A pair of 

 vascular ridges extend out on each side of the valve nearly opposite to the 

 central muscle scars ; at the end of this ridge there appears to be a 

 minute muscle scar. Another pair of shorter ridges outside of these, 

 mark the position of the main lateral muscles. 



