Conorbis mcnairyensis (Wade, 1917)

 

 

Description by Wade: Shell very small and biconic in outline; spire elevated, its altitude equal to about half that of the entire shell; whorls abruptly shouldered or strongly tabulated, the maximum diameter falling in front of the median horizontal, volutions closely appressed and increasing gradually in size, probably four in number in a perfect individual; sculpture subdued and irregular; well-defined axial costle not developed; spirals low and crowded, about six in number on the last but one, and more than sixteen on the last, spirals crossed by numerous irregular, sharply incised incremental lines which give the surface of the shell a subeancellate aspect; suture impressed; body shouldered posteriorly and sloping gently and evenly in front; aperture narrow; margin of outer lip broken away; inner lip concave medially; columella slightly flexed near the anterior extremity; umbilicus indicated by a narrow depression along the outer margin of the reflected inner lip.

 

Dimensions: Height 4.3 mm.; maximum diameter 2.5 mm.

 

This form is represented by a single specimen. The species has been referred to the genus Conorbis since it shows all the generic features revealed in the type of the genus, Conus dormitor (Sowerby) from the Eocene of western Europe. The Tennessee form is probably the first typical Conorbis to be reported from the Upper Cretaceous.

 

 

Powell (2) retained this species Conorbis mcnairyensis (Wade, 1917) in Conorbis and thus extended the range of that genus from Cretaceous to Recent.

However, the shell aperture of Conorbis mcnairyensis is not straight and its sides are not parallel, and there is no evidence either of the exhalent sinus or the arcuate outer lip characteristic of the Turridae, including Conorbinae.

 

Sohl (1964) retained Conorbis mcnairyensis in the Turridae, questionably assigning it to Cryptoconus (3).

 

 

 

 

Conorbis mcnairyensis (1)

mm. 4,3 x 2,5

 

 

 

 

 

 

 

 

 


Bibliografia Consultata

 

·        (1) - Bruce Wade (1917) “New and little known gastropoda from the Upper Cretaceous of Tennessee”

·        (2) - POWELL, A. W. , 1966, The molluscan families Speightiidae and Turridae. Bulletin of the Auckland Institute and Museum, 2, 1-188

·        (3) - JEAN-MICHEL PACAUD & KAI INGEMANN SCHNETLER (1999) “ Revision of the gastropod family Pseudolividae from the Paleocene of West Greenland and Denmark“