340 Annals of the Carnegie Museum. 



19. Modiolopsis subquadrilateralis Hudson. 



Modiolopsis subquadrilateralis Hudson, Report ot the N. Y. State Paleontologist 

 for 1903 (1904), p. 286, Pi. 4, figs. 8, 9. 

 This is a small shell, with smooth, convex valves. It is described 

 in detail in Professor Hudson's recent paper. 



20. Modiolopsis sowteri Raymond. (Plate XXX, figures 21, 22.) 



Modiolopsis sowteri Raymond, American Journal of Science (Ser. 4), Vol. XX, 1905, 

 P- 374- 

 One of the most common and best preserved pelecypods occurring 

 in the Aylmer formation is a species of Modiolopsis to which I gave 

 the specific name, sowteri, in honor of T. W. E. Sowter, Esq., of 

 Aylmer, Quebec, who has given much close attention to the study 

 of the Aylmer formation, and who collected a large part of the many 

 new species which have been described from his native town. 



Description. 



Shell of medium size for the genus, rather convex, with a strong 

 ridge running from the beak to the lower posterior angle. Toward 

 the front is a slight depression, running from just ahead of the beaks 

 a little backward to the basal margin. In front of the beak is a very 

 deeply impressed anterior muscle scar, which on the internal cast, is 

 represented by a rounded, conical elevation. The posterior scar is 

 large, and close to the hinge line. One specimen is 51 mm. long and 

 28 mm. high; another 33 mm. long and 20 mm. high. 



Locality, — From the Aylmer sandstone (Upper Chazy), about sixty 

 feet above the high water mark of Lake Deschenes, at Aylmer, 

 Quebec. Collected by T. W. E. Sowter. 



Appendix. 



The following species were described as coming from the Chazy, 

 but really belong to the overlying formation, the Pamelia, which is 

 of Lower Black River age. 



21. Ctenodonta parvidens Raymond. (Plate XXIX, figures 7, 8.) 



Clenodonla parvidens Raymond, American Journal of Science (Ser. 4), Vol. XX, 

 1905, p. 373; Whiteaves. Ottawa Naturalist, Vol. XXII, 1908, p. 113, pi. 3, 

 fig. 16. 



One of the commonest species in the shale and sandstone of the 



