162 



PALAEONTOLOGY. 



SIPHONARIID^. 



? Genus ANISOMYON, M. & H. 



ANISOMYON SEXSULCATUS, M. & H.? 



Helcion sexsulcatus, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIIT, 08. 

 Anisomyon sexsulcatns, Meek and Hayden (1860), Am. Jour. Sci., XXXVIII (2d ser.), 

 35.— Meek (1876), Palseont. Upper Missouri, 293, pL 18, figs. 8 a, b. 



Fig. 4. 



Fig. 5. 



Anisomyon sexsulcatus. 



Fig. 4. An internal cast as seen 



from above — (nat. size). 

 Fig. 5. A side-view of same. 



The specimen I have here referred doubtfully 

 to the above species is smaller than the original 

 type of the same, being but little more than half 

 the linear dimensions of that species. It also has 

 its apex proportionally a little higher, and the ante- 

 rior slope slightly convex near the apex, instead of 

 concave ; while it shows on the internal cast an 

 obscure mesial carina down the posterior slope, 

 not seen on the cast of the type of A. sexsulcatus. It shows the six radiating 

 furrows, however, exactly as in that species, and agrees so A^ery nearly 

 in all other known characters that I have concluded to refer it provisionally 

 to the same. 



The original type-specimen of A. sexsulcatus is an imperfect cast of the 

 interior, retaining only tliin films of the inner layer of the shell. That now 

 before me is also an internal cast, but retains some fragments of the shell 

 near the margin, and one of these shows that there is, as I had long since 

 conjectured, a narrow furrow on the outer surface of the shell over each of 

 those seen on the internal cast. These fragments of the shell, although 

 apparently not worn, show only obscure marks of growth. 



I suspect that a good series of specimens may show this shell to be a 

 distinct species from A. sexsulcatus, of smaller size. If so, it may be called 

 A. Wyomingensis, 



Locality and position. — Outer sandstone ridge southeast of La Porte, 

 Colorado ; Fox Hills Group of the Upper Missouri Cretaceous series. 



