342 PALEONTOLOGY OF ILLINOIS. 



of a Modiola. Anterior margin sinuous, but not gaping in the 

 middle, and forming a kind of lobe above in front of the beaks 

 and umbonal ridges; beaks compressed, small, very oblique, 

 not quite terminal, depressed ; umbonal ridge prominent, ex- 

 tending from the beaks obliquely backwards and downwards 

 in advance of the middle of the valves, gradually dying out at 

 the anterior ventral margin ; hinge line equaling at least half 

 the entire length of the valves, straight, but passing into the 

 posterior margin without forming a perceptible angle ; posterior 

 side compressed, cuneate, and forming in outline a graceful 

 descending curve to the narrowly rounded posterior basal ex- 

 tremity. Cardinal area very narrow, with not more than two 

 or three linear cartilage furrows. Surface marked with fine 

 obscure concentric striae, and a few not very apparent stronger 

 marks of growth. Length, 1.08 inch — measuring obliquely 

 from the umbonal extremity to the posterior basal margin; 

 breadth at right angles to the longer axis, 0.51 inch; convexity 

 of the two valves, 0.37 inch. 



This species differs from M. recta, Shumard,* and M. perattenuata, Meek and 

 Hayden,f in having its beaks not quite terminal, and its anterior margin above 

 the middle, projecting in front of the beaks and umbonal ridge as a kind of lobe.J 

 Its beaks are also much less attenuate and pointed. It also differs from 31. recta 

 in not having its umbonal ridge "angulated" nor its interior margins inflected 

 at an acute angle with the plane of the body of the shell, while none of the 

 specimens show any traces of the fine radiating striae sometimes seen on that 

 species. From Myalina squamosa (=-Mytilus squamosus, Sowerby), some varie- 

 ties of which (supposing that shell to vary to the extent represented by Prof. 

 King) it resembles, it will be readily distinguished by its much narrower cardi- 

 nal area. It is also a much less variable species. 



Locality and position : Same as last. 



* St. Louis Academy of Sciences, i, p. 212. f Trans. Albany Inst., iv, March, 1858. 

 % This lobe is partly hidden by the matrix, in the specimen figured by Prof. McChesney. 



