248 Annals of the Carnegie Museum. 



In the pedicle valve there is a wide, deeply concave spondylium, 

 supported by a strong median septum. This spondylium was the 

 place of attachment of the adductor and diductor muscles, but the scars 

 left by them are very faint. Beneath the spondylium and extending 

 nearly to the front of the shell are the radial markings of the vascular 

 system. The delthyrium is very wide, and was covered by a convex 

 deltidium, traces of which are seldom preserved in the specimens so 

 far collected. 



The area of the brachial valve is crossed obliquely by two grooves 

 bounded by small lamellae, forming shallow dental sockets. At the 

 middle line is a narrow, sharp cardinal process, in front of which is the 

 low median septum. On either side of the septum are two large, 

 deeply impressed scars, and at its anterior end, two small scars. The 

 large adductor muscles must have been necessary in order to hold 

 the valves together, as the teeth and sockets are rudimentary. 



Locality. — This species is abundant on the eastern side of Valcour 

 Island, and less common at Bluff Point, and Chazy. It is probaby 

 one of the species which has been identified as Orthis costalis. 



31. Clitambonites porcia (Billings). 



(Plate XXXVI, figures 15, 16.) 

 Orthis porcia Billings, 1859. Canadian Naturalist and Geologist, Vol. IV, p. 439, 



figs. 16-18. 

 Orthis porcia Billings, 1863. Geology of Canada, p. 130, fig. 58. 



An examination of the type of this species, which was made possible 

 by the kindness of the late Dr. Whiteaves, shows that the specimen 

 described by Billings was the pedicle valve of a Clitambonites. At the 

 apex and along the edges of the delthyrium there still remain portions 

 of the deltidium, and it required only a slight amount of development 

 to reveal the presence of a spondylium. The specimen differs from a 

 pedicle valve of Clitambonites vmlticostus in having a narrower delti- 

 dium and spondylium, and in having much coarser striae. The 

 specimen is 6.25 mm. long, 8 mm. wide, and 3 mm. high at the apex. 



Locality. — -Two miles south of Montreal, Canada. 



Genus Orthidium Hall and Clarke. 

 32. Orthidium ? lamellosum Raymond. 



(Plate XXXVI, figures 17, 18.) 



Orthidium lamellosum Raymond, 1905. American Journal of Science, Series 4, 

 Vol. XX, p. 371. 



