56 KEW TORE STATE MUSEUM 



Thence forward the slope is much more abrupt. The brachial valve 

 conforms in contour with its opposite. 



The cardinal area is narrow, the denticulations on the pedicle-valve 

 quite small. 



The ornamentation of the valves is, as we have just observed, a 

 series of alternating filiform striae with a group of two to six smaller 

 striae in the intervals. These striae multiply rapidly by bifurcation 

 and intercalation, and the fascicles become increased with considerable 

 irregularity. Immature shells of the species may show only these 

 characters and in this condition represent the normal state of Brach. 

 varistriatum, but at maturity the high convexity and abrupt an 

 terior slope is added, and on this anterior surface the striation is 

 modified by the rapid increase in number of the larger striae 

 and diminution in size and number of the intervening striae. 

 Thus the aspect of the striation becomes much more uniform on these 

 later parts of the shell. It is to be observed, however, that this 

 modification does not always set in at the same period of shell growth, 

 and we may therefore have shells of incomplete growth showing these 

 adult characters outside of the umbonal region and, on the other hand, 

 large shells with adult convexity, retaining the fasciculate striation of 

 early stages. We observe in the species Brach. schuchertanum 

 the presence of an indistinct and irregular median fold and sinus on 

 pedicle and brachial valves, and some trace of a like feature is to be 

 occasionally seen on old shells of this species. The striae are crossed 

 by very fine, elevated, concentric lines which distinctly cancellate the 

 surface. 



Brachyprion ma jus is not an uncommon member of this 

 fauna. 



Brachyprion schuchertanum, sp. nov. 



Plate 8, fig. 1-7 



1892. Stropheodonta cf. radiata Clarke, op. cit. p. 413 



Shells at full size as large or larger than in Brach. m a j u s . 

 Convexo-concave, rising from the umbones regularly to the middle or 

 antemedian portion of the pedicle-valve and sloping thence with uni- 



