87 



do not form one continuous scar as in these two genera but consist of a 

 number of small isolated cavities. 



It may be that when the internal characters of Phillips' species become 

 well known, these Lower Silurian forms will be referred to a different 

 genus, but until we have some evidence of a generic difference it would 

 not be safe to give them a separate designation. In all external 

 characters they are identical with the Carboniferous forms. 



Metoptoma Niobe. (N. sp.) 



Fig. 38. 



Pig. 39. 



Fig. 38. — Metoptoma Niobe, a, side view; b, view of upper side, 

 39. — M. Nycteis. a, side view ; 6, view of upper side. 



Description. — Oval, subcorneal, apex much elevated, almost directly 

 above (but a Uttle behind) the anterior margin ; posterior margin somewhat 

 narrowly rounded ; sides gently convex ; anterior extremity more narrowly 

 rounded than the posterior. 



On a side view the outline of this shell is subtriangular ; the base 

 and anterior extremity straight and forming an angle with each other 

 only a httle less than 90° ; the dorsal outhne very gently curved from the 

 posterior margin for half the length, beyond which it is not known. 



The apex is not preserved in the only specimen collected but judging 

 from the straightness of the portion of the anterior extremity that remains 

 it is probably not incurved and forms the most elevated point of the shell. 

 Surface apparently with fine concentric striae. Length 14 lines ; width 

 9 lines ; height so far as is kndwn 5 lines, but judging from the shape it is 

 probably 6 or 7 Hnes in a perfect shell. 



Locality and Formation. — PhiUipsburgh, in the County of Missisquoi, 

 Canada East. In the upper part of the Calciferous formation. 



Collector. — B. Billings. 



