139 



VALVES of Obolus discus from Assise E. 1 e. 



Dimensions 

 &c. of the 



r, valves. 



OBOLUS .EQUIPUTEIS, n. sp. PI. VIII, figs, a e. 



Valves corneous equally lenticular, nearly orbicular in outline; urn- Obolus (E.) 

 J sequiputeis 



bones depressed. described. 



Ventral valve with a short, low beak, having a narrow conical pedicle 

 groove. Cardinal area broad. Interior. Opposite the pedicle groove is a 

 small shallow pit, perhaps marking the point of attachment of the ped- 

 icle muscle. The lozenge heart-shaped area, or callus in front, is bordered 

 by a strong furrow, outside of which, on each side in front, is the 

 triangular imprint of the central group of muscles, In front of the 

 middle of the valve, near the axial line are two minute pits, extending 

 back from these across the heart-shaped area is a faint slender median 

 ridge. Two strongly marked ridges, diverging from the umbonal region, 

 separate the lateral group of muscles from the depression of the visceral 

 cavity ; these muscle scars extend forward on each side of the valve from 

 the cardinal region as far as the centre of the heart-shaped area. In 

 front of the ridges above named, are the grooves of the vascular trunks, 

 which sweep around towards the front of the valve parallel to its margin. 



The dorsal valve has a nearly orbicular outline, and a rather prominent, 

 broad umbonal region. Interior. This shows a broad and long cardinal 

 area. At the back of the valve, close to the hinge on each side of the 

 umbonal region, are small scars apparently due to the posterior adductor- 

 From the hinge on each side of the median line, a sharp ridge runs forward 



