602 



S. So BUCKMAN ON AMMONITES PROM 



ture, back to front, 4*50 inches, across abont 5J inches, inclu- 

 sion 0-80 inch. 



The aperture is, as nearly as possible, an equilateral triangle 

 with a small piece out, caused by the inclusion. The ventral area, 

 however, is a good deal rounded. 



Perisphinctes ptom^um (d'Orb.). 



Ammonites pygmceus, d'Orb. Terr. Jur. pi. 129. figs. 12, 13. 

 I have one specimen of this species from the neighbourhood. 



Perisphinctes Martinsii (d'Orb.). 



1845. Ammonites Martinsii, d'Orb. Terr. Jurass. pi. 125. 



1854. A. Martinsii (d'Orb.), Morris, Catalogue, p. 293. 



1856. A. Martinsii (d'Orb.), Oppel, Juraformation, p. 387. 



Localities. Zone of Cosmoceras Parhinsoni at Halfway House, 

 Bradford Abbas, Sherborne, and Burton Bradstock, but is rather 

 scarce. 



[At Oborne, in the Humpliriesiamim zone, we find a very thin flat 

 Ammonite with the furrows well marked. It is far more involute 

 than Perisphinctes Martinsii, the amount of involution being nearly 

 half the preceding whorl. It has a semilunar mouth-border, which 

 projects well forward on the ventral margin. 



It has hitherto been put down as the same as P. Martinsii ; but 

 I feel certain that it should be separated as distinct from it, both on 

 account of its stratigraphical position and also its lobes and other 

 features. I propose for it the name Perisphinctes Davidsoni, in com- 

 pliment to Thos. Davidson, Esq., F.R.S.] 



I have one specimen of Perisph. Martinsii, d'Orb., with the termi- 

 nation. It has two long ears, the inner edges of which project well 

 forward till the}' touch the inner whorl. This termination is well 

 represented by d'Orbigny, Terr. Jurass. pi. 125. fig. 1. The termi- 

 nation represented in fig. 3 may possibly have been taken from a 

 specimen of Perisph. Davidsoni, S. S. Buckm. 



Harpoceras Sowerbyi (Miller). 



1821. Ammonites Sowerbyi (Miller), Sow. Min. Conch, tab. 213. 



1821. A. Brownii, Sow. Min. Conch, tab. 263. figs. 4, 5. 



1845. A. Sowerbyi (Miller), var., d'Orb. Terr. Jurass. pi. 119. 



1849. A. Sowerbyi JMiUeY), Quenstedt. Ceph. p. 374. 



1854. A. Soiverbyi (Miller), Morris, Catalogue, p. 295. 



1867. A. Sowerbyi (Miller), var., Waagen, Geogn. Palaont. Beitriige, 

 pi. 27. fig. 2. 



1856. A. Soiverbyi (Miller), Oppel, Juraformation, p. 369, no. 20. 



The figure given by d'Orbigny, pi. 119, represents a variety of 

 this species, and it differs from it in several points. Waagen has 

 also figured, pi. 27. fig. 6, a peculiar variety. 



Localities Sfc. Harpoceras Soiverbyi is a scarce fossil, the species 

 which has been put down by that name as occurring in this district 

 being really Harp, adicrum (Waagen). The chief characteristics of 

 Harp. Sowerbyi are a very large keel, and sides which slope in gra- 



