170 [September, 



6. Cerithium. 



1. C. nodosus. Shell turrited ; whorls six, convex, crossed by distant, strong 

 ribs, swelled into nodes on the middle of the whorls j^ body whorl with re- 

 volving impressed lines below. 



Locality, Alabama. 



LAMELLIBRANCHIA. 



1. Teredo. 



1. T. calamus. Shell thin, cylindrical, transversely wrinkled, large. 



Diameter, 0.5 in. 



Locality, Columbus, Mississippi. Dr. Spillman. 



2. Panop^sa. 



1. P. cretacea. Shell oblong ; buccal side shorter, slightly cuneate, rounded; 

 anal side undulating, gaping. 

 Length, 1.5 in. 

 The only species known in our cretaceous rocks. 



3. Pholadomya. 



1. P. tenua. Shell thin, oblong, somewhat inflated, radically ribbed ; ribs 

 obsolete on the anal side ; umbones prominent. 



Length, 1 inch. 



4. Corbula. 



1. C caudata. Shell oblong ; somewhat equivalve, inflated, concentrically 

 striate ; buccal side broadly rounded ; anal side abruptly contracted and pro- 

 duced ; umbones incurved, not opposite. 



Locality, Noxubie. Mr. Richardson. 



5. Cardittm. 



1. C. hemicy elicits. Shell thin, very inequilateral, radically ribbed ; ribs 

 numerous, umbones somewhat depressed. 



Distinguished from our other species by the inequilateral valves. 

 Locality, Alabama. 



6. Arca. 



1. A. (Cueullcsa) ungula. Shell cordate, inflated, short, thickness greater 

 than the length or height ; ligament area very wide ; umbones incurved, distant. 

 Locality, Alabama. 



7. Inoceramus. 



1. I. biformis. Shell thin, compressed, umbonial portion with regular concen- 

 tric folds or undulations, and fine striae; paleal region smooth, without undula- 

 tions, covered with very regular, closely arranged, impressed concentric lines. 



This is the largest of our species, being one foot in diameter. Resembles I. 

 Nebrascejisis, Owen; but is distinguished from it by the greater fliguity of the 

 folds, and by the close, regular lines. 



Locality, Cahawba, Alabama. 



2. I. gibbus. 



Syn. I. Barabini, Mort. var. 



Shell very thin, somewhat inequivalve, semicircular, convex ; concentrically 

 plaited, plaits irregular; hinge line straight. 



A fragment of this species is figured in the " Synopsis," as a variety of I. 

 Barabini, but 7. Barabini belongs to a division of the genus that has the 

 valves nearly equilateral. 



