54 Prof. F. M'Coy on some new Silurian MoUusca. 



resemble the recent Anodons, from which there being but two 

 simple adductor impressions separates them. They differ from 

 Modiolopsis (or Cypricardites) in their rotundato-quadrate com- 

 pressed form, and the posterior adductor impression like the an- 

 terior one, and they have no trace of the byssiferous sinus so 

 common in that group between the body of the shell and the 

 anterior side : from Schizodus {Myaphoria), with which Prof. King 

 seems to have blended them, they are distinguished by the long, 

 slender, posterior cartilage plate or lateral tooth a little below the 

 hinge-line. Except in form they are identical with Clidophorus, 

 and should be considered but as a subgenus thereof, distinguished 

 fi-om those long narrow types by their broad rounded or oblique 

 axe-like form, more prominent beaks, and less marked clavicular 

 ridge. From the figure of Microdon bellastria (Conrad) I should 

 have imagined it belonged to the present genus, but his descrip- 

 tion of the hinge renders it probable that this genns is different, 

 and I accordingly give a description of my own clear types, be- 

 sides which the name Miaodon was applied long previously to a 

 genus of fish and one of insects. 



Anodontopsis angustifrons (M'Coy). 



Sp. Char. Longitudinally subtrigonal, compressed (depth of both 

 valves half the width), diagonally subcarinate from the beaks 

 to the respiratory angle ; beaks small but prominent, rather 

 more than one-fourth of the length from the anterior end, 

 which is much narrowed and abruptly compressed beneath the 

 beaks, produced, rounded, not separated fi'om the body of the 

 shell by any sinus ; ventral margin nearly straight ; hinge- 

 line short, slightly elevated, forming a wide compressed pos- 

 terior slope, the margin of which is almost uniformly arched 

 from the beaks to the respiratory angle, which is obtusely 

 pointed; surface nearly smooth, a few obscure concentric 

 wrinkles of growth near the margin. Width from beak to ven- 

 tral margin 6 lines, length 1 inch 2 lines, width from middle 

 of dorsal to opposite ventral mai-gin -^£^, length of anterior 

 end j^^^. Pallial and muscular impressions as in the generic 

 characters. 



The more arched and elevated hinge-line and nan-ow anterior 

 side separate this from the Pullastra Icevis (Sow.), which seems 

 to belong to the same genus ; and the contracted anterior end 

 and greater length separate it from the A. quadratus (M'Coy). 

 The posterior lateral tooth or plate extends almost to the end of 

 the hinge-line and close to it. 



Common at Benson Knot, Kendal, Westmoreland, and Kirkby 

 Moor, Kendal, Westmoreland. 



{Cnl. University of Cambridge.) 



