120 



This species 

 compared 

 with O. 

 Quenstedti. 



Original 







There may be some question as to the interpretation of the muscle 

 scars of the dorsal valve of Lingulella Selwyni given in the preceding 

 description, which is based on that of Lingula. But if it be assumed 

 that the three principal posterior scars of the dorsal valve represent 

 respectively i, I and k, the two latter will closely accord with those of 

 bolus ; but then the posterior outer scar is without analogy in that 

 genus, and the whole group is more closely crowded together. 



Another distinction which appears to be of generic value is the position 

 of the (1) lateral in the ventral valve. In 0. Quenstedti it is at the side 

 of the central scar (A), whereas in L. Selwyni it is at the front of this 

 scar. In consequence of the different arrangement of the group of central 

 scars in this valve in Obolus, the front outline of these scars curves away 

 backward from the front of the visceral callus on each side, but in Lin- 

 gulella it is transverse, or even turns forward from the front of the callus. 

 It results that the whole group of central muscles in Lingulella is strongly 

 triangular. 



The following is the original description of this species quoted from 

 Trans. Roy. Soc. Can. 2d Ser. vol I, Sec. IV. p. 255, pi. I, figs, la and b. 



"LINGULELLA SELWYNI, n. sp., PI. I, Fig la and b. 



The form is sub-ovate, broadly rounded in front, but having nearly 

 straight sides in the posterior half ; the beak of the ventral valve is regu- 

 larly pointed and that of the dorsal bluntly rounded. The ventral valve 

 in its interior, exhibits two large, triangular scars, where the central 

 muscles were attached, one on each side of the rhombic pit in the pos- 

 terior third of the valve. The posterior adductors appear on each side 

 of the hinge area, and there are sliding muscles, exterior to and in front 



