JURASSIC FOSSILS. 45 



of the truncated posterior side. Beaks curving forward. (Hinge 

 and ears unknown.) Surface ornamented with about twelve to 

 fourteen strong, simple, obtuse, radiating plications, which are 

 rather wider than the furrows between, and all curve regularly 

 forward as they approach the beak; those on the anterior side 

 descend from the beaks with an oblicme forward curve. (Finer 

 surface-markings unknown.) 



Diameter from the beaks to the most prominent part of the 

 ventral margin, about 2 inches ; antero-posterior diameter, about 

 the same ; convexity (of right valve), 0.46 inch. 



The only specimen of this shell in the collection is a right valve, which has the 

 point of the beak, both ears (if there Were two), and some of the posterior margin 

 broken away. Hence it is with considerable doubt that I have ventured to refer 

 it to this genus; and it is quite probable the above description may be found to 

 require modification, when entire specimens can be obtained. Its most marked 

 peculiarities, supposing it to be a true Lima, are the forward curvature of its beaks 

 and costse, and the prominence of its posterior umbonal slopes. 



These characters, together with the strong radiating costD3, give the shell much 

 the aspect of some types of Cardita, to which genus I should have been inclined to 

 refer it, provisionally, were it not for the fact that it shows unmistakable remains 

 of a flattened ear behind the beak. The specimen is not in a condition to show 

 the size or form of this ear ; but it was evidently very flat, and separated from the 

 prominent posterior umbonal slopes by an oblique sulcus, formed by the inflection 

 of the truncated posterior side of the valves. The specimen gives no indications 

 of an anterior gap, or of a defined lunule. 



In some respects, this species resembles L. striata of Deshayes, and L. radiata, 

 G-oldfuss, from the Muschelkalk ; but it differs from both in the anterior curva- 

 ture of its beaks and costse, as well as in its cuneate anterior side, prominent 

 posterior umbonal slopes, and flattened posterior ear. 



If we go back of the date of the binomial system of nomenclature established 

 by Linnseus, in carrying out the law of priority, Klein's name Radula would have 

 to be adopted for the genus Lima; and the names of this and the foregoing species 

 would become Radula sinuata, Radula cuneata, and Radula recticostata. Or, if it 

 is considered desirable to separate such fossil species from the typical Limas of 

 more modern date, Sowerby's name, Plagiostoma would have to be adopted, and 

 the names would be Plagiostoma sinuata, P. cuneata, and P. recticostata; unless 

 some of our shells, as elsewhere suggested, may constitute a new genus. 



