110 The Ottawa Naturalist [Sept. 



MoDioLOPSis fab^formis, Raymond. 

 Plate III, figs. 7, 8 and 9. 



Modiolopsis fabczformis, Raymond. 1905. Amer. Journ. Sci., Fourth 

 Series, Vol. XX, p. 374. 



A few specimens that are probably referable to this species, 

 though the dorsal margin of each is not quite so high posteriorly 

 as is that of a typical specimen of M . jabcejormis, a right valve 

 from Valcour Island, kindly lent to the writer by Mr. Raymond. 

 Three of the best of these specimens from the Hog's Back are 

 figured on Plate III. They may be described as follows: — 



Shell very small, rather strongly convex, most prominent 

 and tumid on the posterior umbonal slopes, with a faint, wide, 

 shallow and oblique depression in front of them ; maximum 

 thickness through the closed valves nearly as great as their 

 maximum height; valves elongated, twice as long as high and 

 very inequilateral. 



Anterior portion of the valves short, narrowly rounded at 

 its extremitv below; posterior portion thereof much longer 

 and a little higher and deeper than the anterior, its extremity 

 either obliquely subtruncate above and apparently bluntly 

 pointed below, as in figs. 7 and 9, or evenly rounded, as in 

 fig. 8. Ventral margin very shallowly, and in some cases (fig. 

 7) rather obliquely concave anteriorly, and gently and broadly 

 convex behind. Superior border descending rapidly and 

 obliquely in front of the beaks, nearly straight and horizontal 

 behind thein; valves highest and deepest at the posterior 

 termination of the hinge line, in consequence of the slight 

 convexity of the ventral margin posteriorly; umbones low, 

 obtuse; beaks small, depressed, incurved, and placed at a short 

 distance from the anterior end. 



Test unknown ; surface of the cast marked with a few con- 

 centric lines of growth. Hinge dentition and muscular impres- 

 sions unknown, 



The original of figure 7, on Plate III, is a cast of the interior 

 of both valves. The specimen represented by figure 8, on the 

 same plate, is a cast of the interior of a right valve, with a some- 

 what straighter ventral margin, and more regularly rounded 

 posterior extremity. In its size and marginal contour this 

 specimen closely resembles the Trenton fossil figured by Hall 

 as a "large and characteristic form" of Modiolopsis faba 

 (Conrad) on Plate 35, fig. 6 a, of the first volume of the Palaeon- 

 tology of the State of New York. The cast of the interior of 

 a right valve represented by fig. 9 on Plate III, is rather like 



