580 



GENUS SCAPHITES. 



difference between the form of the Scaphite from that of the Ammonite, to which it approaches the nearest, 

 is sufficient, I conceive, to show the propriety of a separation. I acknowledge that I was at first disposed 

 to consider it as a monstrosity ; supposing that the animal had by some accident been misdirected in its 

 operations of forming its shell, and had thereby been led to the formation of it in this uncommon shape. 

 A closer examination of the shell, however, set aside this opinion; for I then noticed the tubercles on 

 the sides of the straight part, which did not appear at all in the spiral, and but faintly in the recurved 

 part." 



Mantell, in his Medals of Creation, edition of 1844, gives the following definition of a Scaphite. 



" Small chambered shells, of a boat-like form, with the inner whorls coiled up in a spire, and half hidden 

 by the outer chamber, which becomes contracted and recurved on itself, is destitute of septse, and termi- 

 nates in an oval or transverse mouth. The syphon is dorsal." 



D'Orbigny, in his Palajontologie Universelle, 1851, gives also a definition of this genus in the follow- 

 ing words : 



" Coquillc formee d'une spirale reguliere, enroulee sur la meme plan, a tours contigus, crossant regulierc- 

 ment jusqu'au dernier tour, qui se detache des autres et sc projette en crosse plus ou moins allongee." 



On applying these definitions and distinctions to the chambered convoluted shells of the cretaceous for- 

 mation of Nebraska, they are found to be all at fault. Fig. 4, of Tab. VII., and fig. 4, Tab. VIII. of 

 this Report, and figs. 2 and 3, PI. 16, and fig. 4, PI. 19, of Morton's Synopsis of Organic Remains of the 

 Cretaceous Group, all go to prove that Parkinson's principal distinction, by the tubercles, is incorrect; the 

 tubercles being equally distinct upon the spiral part and the deflected terminal portion, as on the straight 

 part; indeed, in fig. 2, PL 16, of Morton, the tubercles are even more distinct on the deflected portion. 



The boat-shaped form of the shell, caused by the deflection on itself of the last half whorl, is equally 

 unsatisfactory, as Nebraska affords all possible gradations from the true boat-shaped form of fig. 4, Tab. 

 VIII., to the regular Ammonite-whorl, figs. 1, 2, 3, 5, 6, and 7, of Tab. VIII. It was at first supposed 

 that a satisfactory distinction could be found in the absence of serrated septse in the last half or quarter 

 whorl ; but, on further examination, even this distinction was found to fail, since in two beautiful speci- 

 mens of A. Mantelli, of Sowerby, in the collection of the Academy of Natural Sciences of Philadelphia, 

 and in several of the chambered shells of Nebraska, the serrated sutures of the septa; were found to be 

 entirely absent in the last half volution, though the shells have the normal Ammonite whorl. Now the 

 syphon being dorsal both in the Ammonite and Scapihite, and the serrations of the sutured septa; perfectly 

 analogous, I find myself completely at a loss to establish any generic distinction, that will enable me to 

 decide whether certain fossils from Nebraska are Ammonites or Scaphites ; and this is the very reason 

 why we find D'Orbigny in his Prodrome referring Ammonites Conradi of Morton to the genus Scaphites, 

 and why Morton was so puzzled in determining the species brought by Nicollet from the Upper Missouri. 

 Unless some far more persistent character can be found on which to establish the genus Scaphites, than 

 has yet been presented to us by palaeontologists, the genus must be entirely abandoned and merged in 

 the genus Ammonite, and the boat-shaped convolution and absence of septse in the terminal part, must be 

 regarded as specific and not generic distinctions. 



SCAPHITES (AMMONITES?) COMPRIMUS. (N. S.) 

 (Tab. VII., fig. 4.) 



Specific character. — Shell compressed and slightly boat-shaped. One volution visible, the rest con- 

 cealed in the outer chamber. Surface ornamented with slightly curved costa;, which, on the chambered 

 portion of the shell, are more than twice as far apart as on the terminal, deflected, non-camcrated part. 

 Every second or third rib runs to the inner margin ; the intermediate ribs are formed by bifurcations, 

 which commence one-fourth or one-half the distance towards the periphery. A row of small, pointed 

 tubercles, on either margin of the flattened dorsum ; a row of flatter and more obscure tubercles, one- 

 fourth of the distance from the inner margin of the convolutions. 



Dimensions. — Longest diameter, three inches ; shortest, two and a half; greatest thickness, j 7 0 of an 

 inch. 



Locality. — Fox Hills, Nebraska. 



