44 FOSSIL MOLLUSCA OF THE CHALK. 



32. Ammonites rusticus, Sowerby. Plate XX, fig. 1. 



Ammonites rusticus, Sowerby. Min. Conch-, t. 177. 



— — D'Orbiy?iy. Paleont. Franc. Terr. Cret., t. Ill, figs. 1 and 2. 



A. testa discoided, tuberculatd .■ anfractibus paucis, rotundatis •■ tuberculis 4 seriatis ; 

 2 lateralibus distantibus, maximis, conicis ; 2 dorsalibus minor ibus, depressis, numerosis : 

 umbilico maximo : dorso rotundato, medio piano. 



Shell discoidal, tuberculated, with few rounded whorls : umbilicus very large, rounded 

 at the sides, exposing three fourths of the inner whorls : tubercles in four rows, viz., one on 

 each side of the whorl, a little above the middle, of ten or twelve very large, conical 

 tubercles ; and two on the back, of about twenty-four smaller, rounded, depressed tuber- 

 cles : aperture nearly round. 



Diameter, 6 inches ; height of last whorl, 2^ inches ; width of aperture, 2 inches. 



A very rare shell, found in the Lower Chalk near Lyme Regis, Dorsetshire. 



33. Ammonites Renevieri, S/iarpe. Plate XX, fig. 2. 



A. testa discoided, compressd : umbilico parvo : aperlurd truncato-hastatd : septorum 

 lobis lateralibus tribus trifidis •• atate juniore, undato-costatd, tuberculatd ; tuberculis 4 

 seriatis, ad umbilicum paucis, majoribus, dorsum versus elongatis, numerosis ; dorso subcari- 

 nato ; adultd omnino laevi, dorso rotundato. 



Shell discoidal, with few flat whorls : umbilicus small, leaving half the inner whorls 

 visible : mouth truncato-hastate : septa with three trifid lateral lobes : at the diameter of 

 four inches, as in the specimen figured, the whorls have their sides ornamented with about 

 ten ribs, each springing from a round tubercle at the edge of the umbilicus, reaching across 

 half the width of the whorl, and then changing to a flattened undulation, which ends at 

 the side of the back in a tubercle, elongated in the direction of the whorl ; alternating with 

 these ribs are similar flattened undulations, ending in similar tubercles : back faintly 

 keeled in the middle : in older specimens the sides are quite smooth, and the back 

 rounded. 



Diameter, 6| inches ; height of last whorl, 3^ inches , width of aperture, 2 inches. 



Found in the Grey Chalk near Bonchurch, Isle of Wight, and near Devizes. 



This species has probably been overlooked from its resemblance to some of the forms 

 of A. varians, from which it is to be distinguished by straighter and more simple ribbing, 

 and by the septa, which have the dorsal saddle divided into three parts, in a manner which 

 rarely occurs in this genus. I have named the species after M. E. Renevier, whose labours 

 among the Cretaceous Rocks of Switzerland deserve our warmest thanks, and who has 

 lately visited this country with the view of helping to bring into harmony the synonymy 

 of the Cretaceous Fossils of England and the Continent. 



