86 



Steiklakdinia DAviDfONii. (Billings.) 1868. 



Plate 6, figs. 1, la, lb, Ic, Id. 



Stricklandinia Davidsonji, (Billings). Geological Magazine, vol. V. p. 59, pi. IV., Jan„ 



1868. 



Desci iptton^'^ ^hell longitudinally ovate ; sides and cardinal extremity 

 rounded ; front usually with a linguiform extension about one-third of the 

 whole width , and of variable length, sometimes simply narrowed from the 

 mid-length to a round point ; greatest width about the middle, or a little 

 above. The valves are almost equally convex. The ventral valve has, in 

 young individv.als^ an obscure mesial sinus, which becomes obsolete with 

 age ; towards the front tl is sinus often gives place to a well- 

 developed fo'd. Some of the large individuals have neither fold nor 

 sinus in this valve. The dorsal valve usually exhibits a fold, which 

 becomes gradi ally broader frcm the beak to the front, where its width is 

 equal to that of the tongue-like projection. The umbones and beaks are 

 so shghtly developed as to give only a very moderate angulation to the 

 cardinal extremity. The hinge-line is about one-third or one-fourth of 

 the whole width, and the areas are, in general, concealed by the close 

 approximation of the beaks when the valves are in place ; but in separated 

 valves the ventral area is well seen ; that of the dorsal valve is linear. 

 In the interior of the ventral valve the mesial septum extends only four 

 lines from the beak in a specimen thirty lines in length ; the triangular 

 chamber is apparently two lines in length. In the dorsal valve the socket 

 plates are very short, and not united : they have, as yet, only been seen by 

 grinding down the beak. The small specimens are smooth, or only exhibit 

 faint indications of ribs ; but as the shell increases in size the ribs become 

 stronger, although in some of the larger (as in the one figured) they are 

 not very distinct. In general there are three or four obscure ribs running 

 straight from the beak to the front ; but on each side of these they curve 

 outwards to the sides. The ribs are faintly developed, and there are from, 

 three to five in the width of three lines at the margin. There are also 

 fine concentric wrinkles, not, however, always visible. 



^' Length of large individuals, three inches ; width, varying from nearly 

 equal to one -fifth less than the length. They occur of all sizes from 

 a length of three fourths of an inch to three inches." 



In nearly all the specimens from Anticosti the surface has a smoothish 

 aspect, although the ribs are always more or less distinctly indicated* 

 Those from the mainland are more strongly ribbed. 



A number of specimens have been collected in Anticosti with scarcely 

 any linguiform projection in the front margin. They are of a smaller 

 size than those figured, and may belong to a distinct species- 



