200 J. Starkie Gardner — On the Gault Aporrhdidce. 



The form of the shell recalls A. Parhinsoni, Mant., with which 

 I have grouped it, but the tuberculated nodes, thickness, and differ- 

 ence in form of wing, and the nodosely keeled appearance of the last 

 whorl, are characters which should have rendered confusion im- 

 possible. 



The following are closely allied species, and are from the Gault : — 

 A. Drunensis, D'Orb.; A.fusiformis, P. and E. ; A. pseudosubulata, 

 d'Orb. ; A. obtusa, P. and C. ; A. Varusensis, d'Orb. 



Aporrhais Parkinsoni, Mantell. PI. VI. Figs. 4, 5, 6, 7. 



Description. — Shell elongated ; the spire forming an angle of about 

 30°, is composed of 9 or 10 convex whorls, which are finely striated spi- 

 rally, the striae being sometimes wider apart in front of the suture. Each 

 whorl is rather irregularly ornamented by 16 to 20 or more, slightly 

 flexuous, slender ribs, which have, though rarely, a tendency to pro- 

 duce varices. The body- whorl is wholly destitute of carinas, and is 

 prolonged in a broad rounded expansion obliquely truncated at the 

 extremity and sinuous at its anterior margin, where it unites with 

 the canal ; there is at the posterior margin a deep sinus equal to 

 half the length of the wing, and above this sinus is a long recurved 

 canaliculated point, in some species nearly equal to the length of the 

 spire and accompanying it, but at a considerable angle. On the 

 wings the continuation of the striae is interrupted and disconnected by 

 rather strongly marked lines of growth crossing them, giving it a 

 somewhat reticulated appearance. The wing is much thinner than 

 in A. marginata. The aperture is narrow, and the anterior canal 

 moderately long. 



The Blackdown specimens are usually of rather smaller size, the 

 ribs slightly more prominent, and with a greater tendency to produce 

 varices. The sinus in the wing is not so deep, and the anterior canal 

 is shorter. 



This species is easily distinguished from all others of the Gault 

 by the rounded appearance of the last whorl, its elongated ribs, and 

 by the form of the wing. The superior prominence of the striae in 

 front of the sutures is not an important character, although considered 

 to be such by Pictet. A number of similar forms are described by 

 Continental authors, none of which appear to be identical with this 

 or the next species. This form of shell seems more especially to 

 characterize the Chalk, representatives being found in all parts of 

 Europe. It is very like A. occidentalis of recent times. 



Distribution. — It is found abundantly at Folkestone, Cambridge, 

 and Blackdown ; also at Sidmouth, and in the ferruginous nodules of 

 Shanklin and other Lower Greensand (Neocomian) localities. Fitton 

 and Mantell give it an extended range in the Chalk, but this range 

 belongs more probably to the next species. On the Continent it is 

 common to the Gault of the Paris and Mediterranean Basins, and 

 to Switzerland. Specimens from St. Florentin have extravagant 

 sutures, and approach A . Ifantelli by the prominence of their ribbing. 



History. — This species was first figured by Parkinson in his 

 Organic Eemains, 1811, vol. iii. p. 63, pi. 5, f. 11, from a Blackdown 

 specimen. In 1822 Mantell, in the Geology of Sussex, p. 72, de- 



