136 CONTRIBUTIONS TO CANADIAN PAL^'HONTOLOGY. 



mum length, eight millimetres ; greatest height, five mm. ; of the other 

 (a left valve) — length, seven millimetres ; height, five mm. 



Liard Eiver, about thirty miles below Devil's Portage, E. G. McCon- 

 nell, 1881 : five detached left valves, one I'ight valve and a small but 

 nearly pei-i'ect cast of the interior of l)oth valves. 



This little shell is only provisionally and very doubtfully referred to 

 the genus Trigonodus of Sandbeiger, on account of a certain general 

 resemblance which it boars, both in shape and surface markings, to 

 the T. Sandbergeri of Alberti, fr(jm the Ti'ias of "Wiirtemburg. 



In the entire absence of any knowledge of the hinge dentition, mus- 

 cular impressions or pallial line of the specimens collected by Mr. 

 McConnell, it is not only doubtful to what genus or family but even to 

 what order they should be I'eferi-ed. On first studying them, the 

 wi'iter was struck with their similarity in external charactei-s to the 

 Nucula elongata of Oborg, from the Trias of Spitsbergen, and Professor 

 Hyatt, who has since examined two of the most perfect ones, thinks 

 that they bear a similar resemblance to two or three species of Nucula 

 fi'om the liluropean Trias, described by Klipstein, Miinstei- and Wiss- 

 man. But, so far as the writer has boon able to obsei-ve, there ai'c no 

 indications or traces of the peculiar, comb-like, interlocking teeth of 

 Nucula in any of the specimens from the Liard Eiver, and there are 

 some reasons for supposing that in the latter the ligament was exter- 

 nal. If the present species should prove to be a Nucula rather than a 

 T'n(/o?iodus, then, in accordance with the known relations of the animal 

 to its shell in living i-epi-esentatives of the former genus, the shorter 

 side of the two would be the posterior, and vice versa, and the beaks 

 would point backwards. 



GASTBEOPODA. 



Margarita triassica. (N. Sp.) 



Plate 17, figs. 8 and S a. 



Shell small, globosely turbinate and about as broad as high : whorls 

 four, increasing rapidly in size, the latter ones ventricose but flattened 

 next to the suture above: spire apparently a little shorter than the 

 outer whorl, which lattei- is depressed in the centre below and rather 

 nari-owly umbilicated, the umbilicus being somewhat deep, with a 

 broadly rounded margin and about one-third the diameter of the base: 

 suture distinct and nearly rectangular : aperture nearly circular but 



