168 CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



of the Survey by Mr. James Deans, of Victoria, V. I. A comparison 

 of these specimens with Richwald's desci'iption and figures of T. inter- 

 media has not tended to confirm the impression that T. Dawsoni is 

 synonymous with that species, but has led to the conclusion that there 

 are apijarently several points of difference between them, which may 

 be thus briefly summarized. 



1. T. Dawsoni mems to have attained to fully twice the size of T. 

 intermedia. According to Bichwald the latter measures one inch and a 

 half in length, fi-om the anterior to the posterior side, and one inch in 

 height, measured from the middle of the inferior mai-gin to that of the 

 dorsal border, whoi-eas the coi-rosponding dimensions in the largest of 

 the three specimens of T. Dawsoni from Skidegate Channel are, length 

 tliree inches and an eighth, height two inches. 



2. The curved ribs of T. intermedia are said to be ornamented with 

 very small spinous nodes, but in T. Daivsoni the nodes on the i-ibs can 

 scarcely be called very small, and they are generally obtusely rounded, 

 though often intersected or partly intersected by the concentric 

 grooves which alternate with the rather crowded raised lines of growth. 



3. There appears to be a slight but constant difference between the 

 sculpture of the broad posterior area of T. Dawsoni and that of T. inter- 

 media. In the last named species this area is described as over-run 

 (parcourue) with oblique, almost vertical, close stri;e, divided into two 

 parts by a horizontal groove. In the figures of T. intermedia these 

 vertical striic are represented as straight, parallel, regular, continuous 

 and devoid of tubercles, and the only tubercles on the postei'ior area 

 appear to be those on the elevated ridge which separates it from the 

 main body of the shell. But, in T. Dawsoni the vertical I'aised lines on 

 the posterior area are often irregularly disposed, interrupted, more or 

 less angularly bent as well as somewhat tuberculated, and there are in- 

 dications of a row of transversely elongated tubercles on each side of 

 the central groove, and of a similar but less distinct row on the sub- 

 angular ridge which separates this area from the escutcheon proper. 



In view of these apparent diffoi'ences between the two forms, it is 

 probably advisable to retain the name originally given to the types 

 from British Columbia, for the specimens from that province and for 

 those now under consideration from the Rocky Mountains. 



AsTARTE Caelottensis, Whiteavcs. 



(Foj- the synonjnny of this species and reference to the publication 

 in which it was figured, see page 1.54 of this Kcport.) 

 One fai]-ly characteristic specimen of a left valve. 



