144 SOME NEW SPECIES OF AMMONITES. 



squared. Ventral area possesses neither keel nor channel, but is 

 rounded. 



The ribs of this species do not join across, but there is a 

 space along the centre of the ventral area into which they unite. 

 The ribs also are not opposite each other, but opposite the inter- 

 mediate spaces on the other side. 



The peculiar furrows, bare space, and raised edge on the inner 

 portion of the whorl are not confined to this species. They are 

 persistent in all specimens, and are found in some other allied 

 species from the Inferior Oolite, as yet, I believe, undescribed. 



Localities. — Bradford Abbas, Dorset, rather scarce. I also 

 possess a specimen labelled Dundry, Somerset. 



Position, zone of Harpoceras Sowerbyi. The specimen figured 

 has the test well preserved, and is about the usual size. This 

 species is named in comj)liment to E. Etheridgo, Esq., F.E.S., 

 F.G.S., &c. 



PERispnixcTES Davidsoni, S. S. Buch., plate iv. 



1S81. „ ,, S. S. Buck., Quart, Jour , Geol. Soc, 



vol. 37, page 602. 



Shell compressed. Whorls numerous, and about one-fourth 

 included. Body chamber about three-parts of a whorl. Orna- 

 mentation, plain rounded ribs ; sometimes bifurcating, some- 

 times not ; also transverse furrows. Ventral area rounded. 

 Mouth-border plain single bend, produced on the ventral area. 

 The test is much thickened just before the extreme end of the 

 border, and consequently produces the depression so \'isible in 

 the cast, as shewn in fig. i. a. This thickening part of the mouth- 

 border is present in nearly all species of Ammonites from the 

 Inferior Oolite, and causes a large depression in the cast. Con- 

 sequently the cast of a mouth -border does not convey any idea of 

 the real mouth-border, and may often lead to erroneous opinions. 

 This thickening would seem to be for the purpose of giving 

 strength. 



The test of the larger specimen is nearly absent, and where it 

 is on is corroded. There are signs of ribs all over the specimen. 



