PHYLLOCERAS BUVIGNIERI. 421 



Phylloceras Buvignieri, d'Orhlgny. PL LXXVI, figs 1 — 3. 



Ammonites Bdtignieri, (VOrbi(jny. Paleont. Fran9., Terr. Jurass., pi. 74, p. 61, 1842. 

 — — Ralph Tate. Proc. Belfast Nat. Field Club, Appendix I. 



Irish Liassic Fossils, p. 6, 18/0. 



Diagnosis. — Shell discoidal, compressed; whorls extremely involute, umbilicus nearly 

 occluded ; sides smooth, convex, covered vv^ith delicate biflexed lines of growth, which 

 become more developed near the border ; siphonal area compressed, subcarinate, marked 

 by angular striae ; aperture compressed, subangulated ; suture-line very complicated, 

 -developing eight lobes. 



Dimensions. — Transverse diameter 145 millimetres ; height of the aperture 80 milli- 

 metres ; greatest width of shell across umbilicus 47 millimetres ; width of umbilicus 5 

 millimetres. 



Description. — This appears to be a very rare Cephalopod, as I have not seen the 

 shell in any of our museums, and find it noticed only in Tate's ' Catalogue of Irish 

 Liassic Fossils.' The specimen figured came into my hands with a collection of Irish 

 Liassic Ammonites obtained in the North of Ireland, and belonging to the Belfast Museum, 

 ^sent to me purposely for the determination of the species. 



The fossil is much injured, still it retains all the specific characters by which this 

 'beautiful Ammonite is distinguished. The shell is very much compressed and not cari- 

 nated ; the sides are smooth and delicately marked with very fine lines of growth, which 

 become more developed and angular on the siphonal area. The whorls are compressed, 

 •convex, and extremely involute ; the last whorl is very deep ; it embraces almost entirely 

 the inner whorls, and nearly occludes the umbilicus, leaving only a small aperture 

 indicating its position (PI. LXXVI, fig. 1). The siphonal area is compressed and bevelled 

 on each side, and rounded in the middle (PI. LXXVI, fig. 2) ; it is marked with well- 

 marked angular striae all directed forward toward the mouth (PI. LXXVI, fig. 1). 



The aperture is lanceolate and much compressed, forming a blunt angle before with 

 two points behind. 



The suture-line is very complex. The septa are symmetrical and divided on each 

 side into eight lobes and into many saddles, formed of unequal parts. The siphonal lobe 

 (fig. 3) is as long as and wider than the principal lateral lobe ; it is much ramified and 

 provided on each side with five branches, two of which are much larger than the others. 

 The siphonal saddle is narrow and very irregularly divided into folioles, of which the 

 central one is trilobed. The principal lateral lobe is formed of many irregular branches, 

 four on the inner and five on the outer side of the lobe. The right lateral saddle, much 

 higher than the siphonal, is much foliated, and terminates in three unequal leaves. The 

 inner lateral lobe has a similar form, but is much smaller and shorter than the 

 |)rincipal lateral lobe. The first auxiliary saddle divides into two, the others are very 



