290 PROCEEDINGS OF THE ACADEMY OF 



tricose ; ribs about 31 ; square, not very prominent, on tbe posterior 

 side divided by an impressed line and posterior to tbe umbo witb an in- 

 termediate raised line ; posterior end emarginate ; cardinal area transversely 

 striated ; hinge line long, and the plates numerous ; disk medially contracted 

 or flattened ; interstices of the ribs transversely striated. 

 Locality. South Carolina. (Miocene.) 



NOETIA Gray. 



N. ponderosa, Say, var. N. carolinensis. Ovato-cuneate, ventricose ; 

 disks flattened submsdially, ribs about 35 in number ; narrow, flattened, 

 divided by an impressed line, except on the anterior side, where they are dis- 

 tinctly lined only near the base, transverse wrinkles between the ribs close 

 and prominent ; these intercostal spaces have each an acute radiating line 

 about the umbonal slope and posteriorly ; basal margin slightly contracted 

 medially. 



Locality. Dauphin Co., North Carolina. (Miocene.) 



Compared to the typical ponderosa it is less ventricose, proportionally 

 longer, and has 35 ribs, whilst the latter has only 26. 



N. ponderosa, Say, is abundant in a fossil state in some localities, and 

 Mr. Tryon has obtained specimens from Cape May, in company with Turritella 

 plebeia, Say, but I have not seen a recent specimen, and suppose it to be an ex- 

 tinct s, ecies. 



STRIARCA, Conrad. 



Equivalve, radiately striate, closed ; hinge area transversely striated, and 

 also the epidermis above it ; hinge line dilated and curved at the ends ; teeth 

 divided into oblique hollow cross plaits. 



S. (Area) centenaria, Say. (Miocene. ) 



The remarkable teeth of this genus distinguish it from all other genera of 

 Arcidce ; the plaits are hollow with parallel laminar sides. 



BARBATIA, Gray. 



Subgenus Granoarca, Conrad. 



Equivalve, gaping anteriorly ; hinges are rather wide and very oblique, 

 with longitudinal grooves angulated under the back ; tooth more or less di- 

 vided into granular plates, posteriorly widely expanded and broken into ir- 

 regular granules. 



A. propatula, C. Miocene Foss., 61, 32, 1. 



CARDITIDiE. 



Subgenus Pteromeris, Conrad. 



Triangular, not oblique, with radiating ribs ; beaks medial ; hinge of left 

 valve, anterior tooth direct or directed slightly towards the anterior margin ; 

 posterior tooth double or bifid. 



Cardita per plan a, C, A fossil of the North American Miocene is the 

 type of this genus, which embraces two fossil and one recent species, all small 

 shells. The other fossil species is Cardita abreviata, C, and the recent P. 

 (Astarte) Jlabella, C, of Florida. 



Family MYTILIDJE. 



MYTILOCONCHA, Conrad. 



Subfalcate, thick ; perlaceons, laminated ; hinge thick, elongated ; pointed 

 at the apex ; an oblique tooth or ridge and parallel furrow throughout the en- 

 tire length of hinge area. 



[June, 



