AMMONITES. 47 



in A. peramplus the dorsal lobe is broad, and the superior lateral lobe thrown in conse- 

 quence farther from the middle of the back. 



The A. Leioesiensis of the Mineral Conchology (my A. leptophyllus) has flatter whorls, 

 a narrower aperture, more distinct ribs, an impressed line along the middle of the back, 

 and the lateral lobes of the septa branching into most complicated subdivisions, in strong 

 contrast with those of the true A. Lewesiensis. Hitherto it has only been found in the 

 Upper Chalk. 



M. D'Orbigny's shell has no resemblance whatever to the A. Lewesiensis of Mantell, 

 and very little to that of Sowerby. It is readily distinguished by a series of numerous 

 short ribs, which, commencing outside the middle of the whorl, are continued towards the 

 middle of the back, where they are suddenly interrupted by an impressed line : the septa 

 are as minutely subdivided as in A. leptophyllus, but the lateral lobes are straight and 

 regularly trifid. It is stated in the 'Paleont. Fran?.,' that this species is found in France, 

 in the Lower Chalk : here I have only received it from the North of Ireland, from a bed 

 which I suspect to belong to the Upper Chalk. In the ' Prodrome de Paleontologie,' 

 p. 212, M. D'Orbigny, has named this species A. GoUevillensis, having learned that it 

 difi'ers from the A. Lewesie7isis of Sowerby, and he removes its habitat from the Terrain 

 Turonien, or Grey Chalk, wherein he quoted it in the ' Paleontologie Fran^aise,' to the 

 Terrain Senonien, or White Chalk. 



M. d'Archiac, in his ' Histoire da Progres de la Geologic,' quotes A. Lewesiensis as 

 peculiar to the Lower Chalk of France ; but I do not know to which of the three species 

 here mentioned he alludes. 



37. Ammonites Wiestii, Sliarpe. Plate XXI, fig. 3. 



A. testa discoided, costatd : anfractihus paucis injlatis : costis 24i — SO promine?itidus, 

 incBqualibus : dorso rotimdato, costato : umbilico parviusculo, prof undo : aperturd semi- 

 ovatd. 



Shell discoidal, with few inflated whorls, ornamented with twenty-four to thirty strong, 

 rounded ribs of unequal length, of which ten rise near the edge of the umbilicus, and the 

 rest near the middle of the side of the whorl, and all are continued across the broad, 

 rounded back, where they incline a little backwards : umbilicus deep and rather small, 

 allowing half of the inner whorls to be seen : opening semi-ovate : the lobes of the septa 

 have not been seen. 



Diameter, 2f inches ; height of the last whorl, 1 J inch ; width of the opening, 1|- inch. 



Very rare in the Chalk with silicious grains, Chardstock, Somersetshire. 



I have seen only one specimen of this elegant Ammoiite, which I have named after its 

 discoverer, J. Wiest, Esq., of Chardstock, from whom I have received great assistance in 

 the preparation of this work. 



