WHiTEAVEs.] FOSSILS OP TEIASSIO ROOKS OP BRITISH COLUMBIA. 131 



seven well-preserved casts of the interior of both valves, with a little 

 of the inner layer of the test remaining, were collected. Three of the 

 latter are evidently casts of adult shells in which the double fold on 

 the front margin is fully developed, while the remaining four are as 

 obviously immature. 



This species seems to differ from T. Humholdtensis in its distinctly 

 biplicated front margin, which is not at all ti-uncated. Accurate draw- 

 ings of two of the best specimens collected by Mr. McConnell have 

 been kindly compared by Dr. 0. A. White with Professors Hall and 

 Whitfield's types of T. Humholdtensis and with C4abb's figures of his 

 type specimens. The double fold at the front in the present species is 

 regarded by Dr. White as a probably good distinguishing character, 

 and he thinks that the drawings sent indicate a proportionately shorter 

 and more robust shell than T. Humholdtensis. He adds, also, that the 

 specimens of Hall and Whitfield and the figures of G-abb show that in 

 T. Humholdtensis "there is a veiy shallow median sulcus, or a mere 

 median flattening of the dorsal valve at the front, with which that f)art 

 of the ventral valve coincides. This gives the seeming truncation of 

 the front to which they refer." 



The indications of a rather long mesial septum in the dorsal valve of 

 T. Liardensis are suggestive of the idea that when the characters of the 

 interior of both valves are better known, the shell may have to be 

 referred to the genus Waldheimia. 



MOLLUSCA. 

 LAMELLIBEANCHIATA. 



MoNOTis suBciRCULARis, Gabb. 

 Plate 17, figs. 3 and 3 a. 



Monotis mhcirc-utaris, Gahh. 1864. Pateont. Californ., vol. I., p. 31, pi. 6, figs. 



29, 29 a. 

 Pseudomonotis suhcircularU, Moj.gisovics. 1880. Arktische Triasfaunen, p. 123. 

 Perhaps=P.s«(rfonionoris ochotica, Keyserling. (Sp.) 



Cfr. Avicula ochotica, Keyserling, 1848, in v. Middeiidorf's " Reise in 

 den aussersten Norden u Osten Siberiens," St. Petersburg, band 1, 

 theil 1, p. 257, taf. 6, fig. 15-17. 

 Pseudomonotis ochotica (Keyserling). Mojsisovics. Op. cit., p. 116, 

 taf. 17, fig. 1-15, and taf. 18, fig. 15-17. 



A few miles above Fossil Point on the Peace River, in lat. 50° 10' and 



