THE FAUNA OF THE ST. JOHN GROUP. 61 



species is in the form of a cast, showing the interior of the central portion, and, around the 

 margins, the cast of the apparently smooth outer siirface. 



" The interior ridge and shiekl-like expansion is of a peculiar character, and lanlike that 

 of any described recent or fossil form known to me. It is so well marked that there is little 

 hesitancy in proposing a new genus for its reception. The genus may be included in the 

 Calyjitranda?, nearest the genus Crepichda, if we compare the shield-like expansion with 

 the shelf or shelly partition of the Crepidula. However close or distant its relations to the 

 latter, it certainly appears to be the representative of the Calyptrœidœ type in the Cam- 

 brian, and adds another form, showing the differentiation of the iuA^ertebrate fauna in the 

 oldest fauna yet known on the American continent." 



The above is Mr. Walcott's deiinition of the genus. As it is an important type, I have 

 given his description, but can add nothing to it, as I have not met with any further 

 examples. Its distinctness from Sfenolheca (Parmophorella) Acadica will be seen by comparing 

 the interior of that shell, as figured in Plate VI. Fig. 10c. From the smaller and typical 

 Stenothecœ it is distinct by its mode of preservation, being entombed with the aperture 

 wide open. The absence of concentric corrugations w^ould also exclude it from this genus. 



Length of aperttire, 3| mm. Width of aperture, 21 mm. 



Horizon and Localil//. This can only be inferred from the association with other 

 species, and from the probable locality, as described by Mr. AValcott. Fine grey shales of 

 Div. l.c (?) at RatclifTe Stream, Simonds. 



VIL— PHYLLOPODA ? 



{Bivalves of uncertai?i relationship.) 



Among the smaller fossils of the strata of Division 1 are two types that appear to belong 

 to the Lamellibranchs or Phyllopods, but which are so minute that their characteristics 

 cannot readily be observed. Of one it may be said that its long, straight hinge-line and 

 weak umbones, as well as its defined border rim, render it possible that it may be a 

 Phyllopod allied to Aptychopsis ; another is described among the Brachiopods, as probably 

 a somewhat distorted Kutorgina ; and there is a third minute organism, whose relation- 

 ship is still more problematical. Although the zoological position of these fossils is thus 

 uncertain, it seems desirable to describe them here, if only for the purpose of calling 

 attention to the existence of such peculiar forms in the early Cambrian rocks. 



LEPIDITTA, n. gen. 



Minute, obliquely semi-circular, or semi-elliptical bivalves, wide on the anterior half 

 of the valve, and having a long, straight hinge line ; umbones in front of the midlength of 

 the hinge, low, or but moderately elevated ; there are indications of a connecting piece, or 

 ligament in front of the hinge line. 



Lepiditta alata, n. sp. (Plate VI. Figs. 16 and 16a.) 

 Valves obliquely semi-elliptical, about one third longer than wide ; hinge line straight ; 



