Vol. 60. ] UPPER JURASSIC AMMONITES. 57 



lobe less. Waagen's Martelli 1 is only distinguished from plicatilis 

 by having fewer ribs. I very much doubt the specific value of this 

 distinction. P. DunikowsJcii, Siem. " includes P. chloroolithicus, 

 Giimb., as figured by Waagen. '' Its whorls are slightly more com- 

 pressed than those of plicatilis, which is therefore intermediate 

 between it and Martelli, having the ribs of the former and the cross- 

 section of the latter. Am. Schilli, Oppel,' is distinguished by the 

 slope of its sides towards the back being much greater. It is also 

 slightly too involute and the second lateral saddle is different. 



I do not propose to enter into the question as to how many of 

 these are good species, but some of them, I think, might with great 

 advantage be reduced to the rank of varieties. 



Remarks. — This specimen is in the Buckland Collection, in the 

 University Museum, Oxford. It bore no label, but no one who has 

 compared it with Sowerby's original figure can doubt its identity. 

 Sowerby's figure is reversed, and somewhat restored : hence the 

 slight differences between it and a photograph of the specimen. 



Perisphinctes biplex (Sow.). (PI. X, rigs. 1 & 2.) [The ' type '- 

 specimen.] 



1821. Ammonites biplex. Sowerl>3', 'Mineral Conchologv ' vol. iii, pi. ccxciii, 

 figs. 1 & 2. 



Description. — In the first place, it is necessary to remark 

 that Sowerby's two figures do not represent parts of the same 

 specimen, as Dr. Siemiradzki believed them to do. The smaller 

 {Joe. cit. fig. 2) is a fragment of a cast in dark, bluish clay, with 

 traces of a nacreous shell still adhering to it, and may be dismissed 

 from our consideration at once. The larger (he. eit. fig. 1) looks 

 as though it had come out of a septarian nodule, probably from the 

 Kimeridge Clay= Sowerby obtained it from the Drift of Suffolk. 1 

 It is preserved in calcite and pyrites, except the body-chamber, 

 which is filled with a somewhat hard, yellowish, compact matrix, 

 and occupies about three-quarters of the last whorl. The whole 

 shell is somewhat distorted. The cross-section of the inner whorls 

 is broader than high, but as the shell grows older this is reversed. 

 There are fifty ribs at a diameter of 100 millimetres. They run 

 slightly forward, and bifurcate just as they pass over on to the back ; 

 one trifurcates, and one remains simple until it reaches the middle 

 of the back, where it unites with both branches of the opposite rib. 

 The suture-line is but partly visible here and there. 



The shell is broken across along the line QR (PI. X, fig. 1) 

 which does not pass through the centre, and when the two parts 

 are put together they form what appears to be an ordinary ammo- 

 nite ; but the cross-section (PL X, fig. 2) shows that this is far 



1 ' Jurassic Cephalopoda of Kutch ' vol. i (1875) pi. lv. figs. 3 a & 3 b. 



2 Palasontographica. vol. xlv (1898) p. 269. 



3 ' Jurassic Cephalopoda of Kutch ' vol. i (1875) pi. 1, figs, oa & ob. 



4 ' Jurassische Ammoniteu ' [atlas] 1862, pi. lxv, figs, la & 7 b. 



5 ' Mineral Conchology ' vol. iii (1821) p. 168. 



