cxliv INFERIOR OOLITE AMMONITES. 



lustration shown in the long projection of the radial line; from Harpoceras 

 (falciferum-gronp), less lateral flexure of the radial line, the simpler suture line; 

 from Pseudolioceras, radial and suture lines. 



Remarks. — The typical forms of the genus are flexiradiate, but two other series 

 are placed here for convenience — one subflexiradiate, the other rectiradiate. 



In many species expansion of the umbilicus by excentric coiling may be 

 observed. It is particularly noticeable in the leptogyral species, taking place 

 while the umbilicus is comparatively open. Thus P. pedicum is subangust- 

 umbilicate in youth and becomes latumbilicate later. One leptogyral species, 

 P. explicatmu, is an exception ; it is latumbilicate throughout, and is an example 

 of concentric coiling. 



In many genera, the concavumbilicate Ammonites for example, and forms of the 

 Hyperlioceras-type, the leptogyral species do not show expansion of umbilicus 

 until angustumbilication has first been obtained, and often, too, not until the ribs 

 have been lost._ In Pseudogrammoceras the expansion of the umbilicus is associated 

 with strong ribbing. 



I. Flexiradiate. 



1. Pseudogrammoceras quadkatum (Quenstedt), (Haug). 



1874. Ammonites Grunowi, Dumortier (non Hauer), Basin du Rhone IV, PI. 



xiv, figs. 6, 7 only. 

 1885. Hildocekas quadkatum, Haug, Monogr. Harp. ; N. Jahrb. Mineral., Beil- 



Bd. iii, p. 638. 

 1887. Ammonites quadratus, Denckmann, Fauna von Doernten ; Abli. G-eol. 



Landesanstalt, VIII, 2, PI. vi, fig. 3. 



Remarks. — There are two series of quadratus-like species — one in which the ribs 

 are distinctly flexed, the other in which they are hardly curved. Dumortier shows 

 both forms (PI. xiv, figs. 6, 7 ; PI. xv, figs. 1, 2). Denckmann shows the flexed form, 

 agreeing with Dumortier's PI. xiv, figs. 6, 7, which I take as type-figure of the 

 present species. I showed a flexed form, but it has coarser ribs (see off. quadratum). 

 Brasil x figured a straight-ribbed form, but it is a very massive shell, quite distinct. 



Locality and Stratum. — Somerset : Shepton Beauchamp, near Ilminster, " Upper 

 Lias." 



2. Pseudogrammoceras aff. quadratum. Plate XXXIV, figs. 6, 7. 



1890. Grammoceras quadratum, This Monogr., PL xxxiv, figs. 6, 7, p. 201. 



Remarks. — This form has coarser ribs than the last, but my material of these 

 two forms is scanty and ill preserved. 



1 " Cepli. Nouv.," 'Bull. Soc. Geol. de Normandie,' xvi, PL i, figs. 9 — 11. 



