SOME NEW DEVONIC FOSSILS 265 



carrying a row of spines, five in number on each side of the beak, 

 the outer ones attaining considerable length. Surface markings 

 consisting of fine threadlike radii increasing rapidly by bifurcation, 

 the striae and intervening grooves being of subequal size. There 

 are three or four of these in I mm. A notable feature is the pre- 

 dominant size of the median stria on this valve. There are also 

 suggestions of concentric or oblique undulation near the cardinal 

 extremities. The surface sometimes shows a broad undefined de- 

 pression with others at the side which may produce a gently un- 

 dulated surface. This, however, is not a persistent feature. The 

 dorsal valve is concave and on the interior shows a small bifurcate 

 cardinal process flush with the cardinal area. The sockets and 

 socket walls rest on a greatly thickened ridge just within the hinge 

 line and subparallel to it. This notable ridge has an abrupt pos- 

 terior slope leading down to the muscular area which is divided by 

 three short and divergent ridges. 



Dimensions. The average example has a length of 16 mm, width 

 of. 23 mm. 



In seeking comparison of this very well defined species with 

 allied forms we may note the following: 



With Chonetes canadensis Billings of the Grande Greve 

 fauna, it is more closely related than with any other, in outline and 

 proportions. Like that it carries a conspicuous median stria. But 

 the species are not to be confounded ; C. aroostookensis is 

 a stouter and heavier shell with a much coarser surface stria- 

 tion and a more convex ventral valve. It is less delicate and 

 tenuous and never attains the notable dimensions of that species. 

 With C. nova-scoticus Hall from the Arisaig series of Nova 

 Scotia, it agrees in the development of the median stria but the 

 resemblance there ceases. Choneteslatusv. Buch as identified 

 by Sowerby from the Tilestones of Horeb Chapel, with which it 

 has been compared, has not even remote relation with it. David- 

 son long ago pointed out that most of the Silurian Chonetes which 

 had been referred to C. 1 a t u s are identical with C. striatellus 

 Dalman but he specially excepted the forms from Horeb Chapel. 

 Neither the one nor the other presents any features for comparison 

 here, the Tilestones shell being small, convex and minutely striate. 

 C. sarcinulatus Schloth., from the Spiriferensandstein and 

 other horizons of the Coblentzian is somewhat similar in form but 

 is more evenly striate, without large median stria and is notably 

 convex. Schnur's variety of this species, planus, from the same 

 beds is little known but appears to be a shell of less width. 



