60 E. Billings — New Species of Stricklandinia, 



convex. The ventral valve has, in young individuals, an ohscure mesial sinus, which 

 becomes obsolete with age ; towards the front this sinus often gives place to a well- 

 developed fold. Some of the large individuals have neither fold nor sinus in this 

 valve. The dorsal valve usually exhibits a fold, which becomes gradually broader 

 from the beak to the front, where its width is equal to that of the tongue-like 

 projection. The umbones and beaks are so slightly 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 ribs running straight from 

 the beak to the front ; but on each side of these they curve outwards to the sides. 

 The ribs are rounded, and there are from tbree 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. 



Ohs. — StricMandinia Davidsonii differs from S. lens, in being more 

 narrowed in front, more strongly ribbed, and in having the area 

 concealed when the two valves are in their natural position. Not- 

 withstanding the variable form of the shell, there are none, in a 

 collection of nearly a hundred specimens, that could be considered 

 specifically identical with any of those figured by Mr. Davidson in 

 the " Monograph," pi. xix. figs. 14:-21. But there is a dorsal valve 

 from the Niagara limestone of Cabot's Head, Lake Huron, exceedingly 

 like fig. 13. It is, however, quite distinct from S. Davidsonii, and I 

 think from S. lens also. 



As before stated the large individuals often have the ribs strongly 

 developed, and curved out to the sides. They thus closely resemble 

 the figure of S. lirata in " Sil. Syst.," pi. xxii, fig. 6. Indeed, I 

 could very nearly re-produce that figure from some of our broken 

 specimens. It is these that I thought could be identified with 

 S. lirata. The small smooth ones I supposed to be S. lens ; but, 

 after seeing Mr. Davidson's figures, I re-examined the whole col- 

 lection, and found that there is a gradual passage from the smooth 

 to the strongly ribbed. The specimen figured (figs. 1-1 c) is about 

 as perfect as a fossil can be, and is a good example of an intermediate 

 form. 



Position and locality. — This species occurs at a number of localities 

 around the coast of the Island of Anticosti, from Jupiter river to 

 East Point. It is most abimdant at South-west Point, where the 

 specimen figured was collected. It is associated with Strophomena 

 rhomhoidalis, S. pecten, S. antiquata, Leptcena transversalis, Orthis 

 Davidsoni, Pentamerus ohlongus, Spirifera plicatella, Leptocoelia 

 {Airy pa) hemispherica, Atrypa reticularis, and many others, mostly 

 new species. The rocks belong to the Anticosti group, division 3, 

 a horizon which is very nearly, if not exactly, that of the Upper 

 Llandovery rocks. It also abounds on the mainland at the Schick- 



