21 
The crural plates are very similar to those of R. capax, as are also the deep 
dental sockets. The large deltidial plates of the pedicle valve are present, 
but so poorly preserved that it is impossible to distinguish the line of 
amalgamation. The teeth are broken, but the thin walls show no sign 
of dental plates. 
Externally R. windermeris is very similar to the large Stony Mountain 
Rhynchotrema identified as a large form of R. capax. There was no 
specimen of R. Windermeris showing the two beaks together, so that 
externally there is a possibility of variation from the very much incurved 
beaks of the Stony Mountain species. Several attempts have been made 
unsuccessfully to eat out the interior of the Stony Mountain Rhynchotrema 
with acid or caustic. The writer is inclined to think, however, that this 
form, if not identical with R . windermeris, is more closely allied to it than 
to R. capax. R. windermeris differs from R. capax in its larger size, in 
being relatively narrower, in its somewhat less rotund proportions, and in 
the initial stage of the stride on the fold. Internally, R. windermeris is 
less robust, the region around the muscle scars and below the teeth being 
much more fragile than the thickened heavy interior of the pedicle valve 
of R. capax. The crural cavity of the brachial valve of the western species 
is more open and does not reach.the bottom of the shell. 
Horizon and Locality. Richmond; Beaverfoot. From the Stoddart 
Creek section of Windermere district, and northeast of mount McMurdo, 
Beaverfoot range, British Columbia. 
j Rhynchotrema increbescens var. occidens n. var. 
Plate IV, figures 6, 7, 8, 9, 10 
Shell quite variable in size and shape, including all gradations from 
a narrow acuminate form to a form as large as, and very similar to, the 
exterior of RR anticostiensis. Most of the specimens, however, are smaller 
than R. increbescens, and the form is characteristically more acuminate and 
less gibbous. As a rule four, though in some cases three, strise on the fold 
and a corresponding number on the sinus. Interior of the pedicle valve 
very similar to R. increbescens. Interior of brachial valve showing a 
variation in the shape and proportions of the different parts. The crural 
plates of the eastern species (Plate IV, figure 5) flattened and grooved 
near the hinge, send into the shell cavity long, slender tongues with slightly 
thickened bifid ends, their direction being at right angles to the hinge- 
plate. The crural plates of the western variety are shorter and threadlike, 
continuing in the plane of the hinge-plate. The hinge-plates of R. 
increbescens are concave and at right angles to the edge of the valve. The 
hinge-plates of the western variety are shorter and narrower with a groove 
in the top. They slope down to the point from which the crural plates 
begin, from which point they turn abruptly downward and backward 
toward the beak, leaving a very short and not deep crural cavity. The 
