INVERTEBRATE PALEONTOLOGY. 83 



showing a broad, deep sulcus starting from each beak, and descending, with a 

 slighl backward obliquity, to (he most sinuous part of the base. Surface 

 with radiating stria'. 



Length, 0..'55 inch; height, 0.19 inch; convexity, about 0.17 inch. 



I have not seen specimens of this little shell showing very clearly the 

 nature of the surface-markings, but Evans and Shumard describe it as having 

 "18 to 20 radiating striae, with accessory ones in the intervals.'' The deep 

 sulcus seen passing downward from the beaks, in our internal casts, is doubt- 

 less nearly as strongly defined on the outer surface of the shell, which seems 

 to be thin. Only faint traces of the radiating stria? are visible on internal 

 casts, excepting immediately at the free margins, to which they impart a 

 crenate appearance. The muscular scars are very faintly marked, perfectly 

 smooth, and only show, on the casts, a scarcely perceptible, very slightly 

 impressed, hair-line, along the anterior side of each posterior scar, and the pos- 

 terior side of the anterior. By cutting away the rock about the hinge, I find 

 it appears to agree exactly with that of Nemodon. 



Specifically, this shell seems to be very nearly related to Area (Macrodon) 

 Evfalensis, Gabb, which Mr. Conrad says is a Nemodon. 



If, as I have suggested, Nemodon should be eventually only considered a 

 subgenus under Macrodon, the name of this species would have to be written 

 Macrodon {Nemodon) sulcatinus, or Parallelodon {Nemodon) sulcatinus. 



Locality and position. — Dr. Evans's specimens of the type of this species 

 were found near Grand River, Dakota; and those here under consideration 

 came from Yellowstone River, 150 miles above its mouth; where they occur 

 in beds containing a mingling of the fossils of the Fort Pierre and Fox Hills 

 groups of the Upper Missouri Cretaceous series. 



Genus CUCULLiEA, Lamarck. 



Synon. — Area (sp.), of many authors. 



Cucullcea, Lamarck (1801), Syst. An., 11G.— Roissy (1805), Moll. VI, 400.— Schumacher (1817), Ess., 



170.— J. Sowerby (1812?), Min. Couch., 1, pi. 67.— Fleming (1828), Brit. An., 382, and 



399.— Morris (1843), Brit. Foss., 84.— Woodward (1856), Man. Conch., 268.— H. and A. 



Adams (1857), Gen. Eecent Shells, II, 539; and of many others. 

 Cucullea, Hanlcy (1844), 111. Cat., 151.— Catlow (1645), Conch. Norn., 48. 

 Idonearca, Conrad (1862), Proceed. Acad. Nat. Sci. Philad., XIV, 289 (as a subgenus of Cucullwa ); 



and (1872), ib., 54. 

 Latiarca, Conrad (1862), ib., 289; and ib. (1872), 53 (as a subgenus of Cucullwa.) 

 Macrodon (sp.), Stoliczka (1871), Paheont. Indica, III, 350 (not Lycett). 

 Grammatodon ? (sp.), Stoliczka (1871), ib. (not Meek and Hayden). 



Etym. — Cucullus, a cap or hood. 

 Type. — Area concamerata, Martini. 



Shell cordate-trapeziforrrrj gibbous, very nearly, or quite equivalve, subequi- 



