MIOCENE MOLLUSCA AND CEUSTACEA. 47 



Arca (Latiarca?) idonea?. 

 Plate VII, fig. 1. 



Arca idonea Conrad: Foss. Shells of the Tert. Form., p. 15, PI. i, fig. 5; Miocene 

 Foss., p. 55, PI. XXIX, fig. 3 ; Emmons, Geol. N. Carolina, 1858, p. 285. 



Latiarca idonea Conrad: Proc. Acad. Nat. Sci., Phil., 1862, p. 289. 



Area idoneaf Heilpriu : Proc. Acad. Nat. Sci., Phil., 1887, pp. 400 and 402. 



Scapharca idonea Courad: Proc. Acad. Nat Sci., Phil., 1862, p. 579; Meek, Check List 

 Miocene Foss., p. 6. 



Arca stiUicldium Conrad: Foss. Shells Tert. Form., PI. i, fig. 3; Miocene Foss., p. 55. 



"Shell siibtrig'onal, thick, diameter equal to about .seven-eighths of the 

 length; ribs about thirty, flattened on the back and angulated on the sides, 

 those on the anterior side with a longitudinal furrow ; ribs of the right valve 

 crenulated over the whole disk; of the left valve distinctly crenulated only 

 on the autei-ior side; crenulations largest on the right valve; beaks distant 

 and very prominent; cardinal line short, a little decurved at the ends; teeth 

 irregular and some of them angulated in the middle; inner margin pro- 

 foundly crenate." (Com-ad, Mioc. Foss., p. 5.5.) 



Two small fragments of shell, presenting much more the characters of a 

 Cardium than of an Arca, come to me among the material from the well- 

 boring at Atlantic City, and are the foundation for the citation of the above 

 species made in the Proceedings of tlie x\cademy of Natural Sciences, Phila- 

 delphia, 1887, pp. 400 and 402. The distance of the ribs from each other is 

 equal to their own diameter and they are rounded on the top, more so than 

 in Area idonea, from the amount of sand wearing which these fragments 

 show, while one of them shows a nodose character of the ribs more charac- 

 teristic of a Cardium than of an Arca. I may be wrong in my sus])icions 

 that they are not fragments of the species to which they are referred, for it 

 is very difficult to assert positively the relations of such small fragments of 

 water-worn shells. 



The specimens are the propei'ty of the Academy of Natural Sciences 

 at Philadelphia, Pa. 



