GASTEROPODA. '• go 



Pleurotomaria sulcomarginata. 



PLATE XIX, FIGS. 8-17. 



Pleurotomaria gidcomarginata, Conrad. Join-. Acad. Nat. Sci. Phil., vol. 8, p. 272, pi. 16, f. 13. 1842. 

 " " " Hall : Descriptions of New Species of Fossils, etc., p. 18. 1861. 



" " " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 46, pi. 5, tigs. 



9 and 10. 1862. 

 " " " " Illustrations of Devonian Fossils : Gasteropoda, pi. 19. 1876. 



Shell depressed-trochiform ; spire moderately elevated ; apex minute. Volu- 

 tions four or five, very depressed-convex on the upper side, gradually 

 enlarging to the last one which becomes somewhat ventricose. Aperture 

 subquadrate, somewhat wider than high, the columella much extended 

 below. 



Surface marked by two distinct, narrow, revolving carinse on each volution, 

 one just below the suture, and the other near the periphery, with finer 

 intermediate striae which are rarely visible ; the entire surface marked by 

 strong, regular and even concentric striae which crenulate the revolving 

 carinse, and, passing over the lower one, bend backward to the concave 

 peripheral band. Suture sometimes sharply canaliculate. 



In entire specimens the apex is very minute, and, when the outer carination 

 is crenulated by the strong concentric striae, the shell has a coronate aspect. 

 This carination, however, is often obsolete on the outer volution, and more 

 rarely on the next above, and the striae then continue uninterruptedly bending 

 backward to the peripheral band, and continuing on the lower side often very 

 nearly of the same strength as above. There is frequently a narrow depressed 

 band just below the peripheral band on the last volution, causing a slight 

 deflection of the striae. The striae are usually finer, and sometimes become 

 nearly obsolete below the outer carination, and more rarely on other parts of 

 the shell, especially near the aperture. 



Mr. Conrad's description of the species is as follows-: 



" Trochiform ; outer margin of the large volution bicarinated, with an inter- 

 mediate sulcus ; volutions with two distant spiral lines, and crossed by oblique 

 striae." 



