STPPI/KMENT.— REYNESIA. 



7. Reynesia benigna, S. Buchman. Suppl., Plate XXII, figs. 10 — 12. 



Description. — Parvicostate, subexcentrumbilicate, compressed around umbilicus. 

 Distinction. — From E. laxa, less marked, less persistent costae ; from R. lepida, 

 more persistent costse ; from both, less concentric umbilicus, less distinct carina. 

 Locality and Stratum. — Dorset: Bradford Abbas, Fossil Bed. 

 Date of Existence. — Discitse hemera. 



Caeinatitabulate. 



In the series of genera now to be described the carinatitabulate periphery is a 

 particular feature of distinction. It is more distinct than the term implies, 

 because the peripheral area is not only flat, but it is, even in the costate stage, 

 levigate — the periphery appears as a flat, smooth band, fairly defined from the 

 lateral area, and on this band is set a more or less prominent carina. The ribs end 

 somewhat abruptly at the edge of this smooth band, and this smoothness 

 forms a distinction from tabulate peripheries formerly noted : such peripheries 

 are costate. Therefore the term would in the present case be more correctly 

 " carinati- and levigati-tabulate." 



Another distinction about this tabulate periphery is its persistence. In other 

 cases the tabulate periphery changes to fastigate, especially as degeneration pro- 

 ceeds and the peripher} r narrows — there being a falling in of the angle between 

 the lateral and peripheral areas. In the present case the tabulation remains until 

 the periphery is extremely acute; the angle between the lateral and peripheral 

 areas being well maintained, often the increased compression rather accentuates 

 the angle than otherwise. 



The carina on the tabulate periphery is found in all degrees of development, 

 from the barely distinct median ridge of Darellella to the pronounced alticarina of 

 Toxolioceras. In the genera where the carina is much developed, the peripheral 

 area looks very like the tongued edge of a matched board. 



When the carina declines, the tabulate passes to the rounded periphery, 

 without any very distinct fastigate stage. 



The relative size of the carina forms a feature of distinction among the 

 following genera ; and to a certain degree it has been used in their grouping. But 

 for the more complete systematic arrangement other features have been taken into 

 account; because owing to the different sizes of the specimens and the allowance 

 that has to be made for keel degeneration, the relative sizes of the carina, 

 when their degrees of differences are not very pronounced, is dimcnlt of com- 

 parison and not easy of description. For the latter purpose the following terms 







