268 PALEONTOLOGY. 



valve is marked by a rather distinct depression, extending from near the 

 beak to the front of the shell, but most marked on the middle of the valve. 

 The striae are rather coarse, somewhat irregular, and present a rugose, 

 knotty appearance; while the upper half of the shell is very distinctly 

 marked by strong, irregular, concentric wrinkles, a little less marked in the 

 central depression. A few of the transverse wrinkles are seen marking the 

 front half of the shell in one specimen, and are broad and less deep than 

 those above. 



The specimens are proportionally longer and narrower than the typical 

 forms of P. semireticulatus ; but the form is such a variable one that it is 

 somewhat difficult to define the limits of its characters. 



Formation and locality. — In the limestone of Lower Carboniferous age, 

 north of Snowstorm Hill, Dry Canon, Oquirrh Mountains, Utah. Collected 

 by J. E. Clayton. 



Peoductus elegans. 



Plate 5, figs. 3-4. 



Compare Productus elegans K & P., Jour. Acad. Nat. Sci. Phila., iii, p. 11, fig. 7. 



There are two specimens of a Productus associated with the preceding, 

 having so much the form and characters of P. elegans N. & P., that, unless 

 from a larger number of individuals other and different features shall be 

 obtained, cannot well be considered as distinct from that one. The form is 

 narrow in the upper part, the hinge-line shorter than the width of the shell 

 below; beak rather small and appfessed; auriculations not very marked ; 

 ventral valve sharply arcuate above and gently curving throughout, with a 

 slight, scarcely defined depression extending from beak to base. Surface 

 of the valve marked by moderately fine but distinctly radiating striae, which, 

 on the better preserved specimen, have an irregular, knotty appearance, 

 caused by the thickening of the striae at the spine-bases. The radiating 

 striae are marked by very fine transverse lines of growth on the forward 

 part of the shell, and on the upper part of the beak and sides of the 

 shell a few obscure transverse wrinkles may be detected. 



There are some slight differences between the specimens, one of them 

 being a little more compressed, giving it a broader form, while the strias are 



