362 S. S. Buchnan — On Jurassic Ammonites. 



Agassiceras Colesi (J. Buckman). 



1845. Ammonites Colesi, J. Buckman, Murchison's Geology of Cheltenham, second 

 edition, p. 89, pi. 12, fig. 2. 



Discoidal, much compressed, strongly carinate. Whorls in youth 

 evidently gibbous, rather strongly and widely costate, gradually 

 becoming flatter-sided, and ornamented with direct, slightly inclining 

 costae, which have a strong forward projection on the periphery, 

 where they are very obscure. The costse, which are slightly swollen 

 at the edge of the inner margin, and again a little more swollen at 

 the bend on the outer area, become practically obsolete towards the 

 end of the whorL (specimen 89 mm. diameter). Periphery fastigate 

 divided by a strong carina. Inner margin well-defined on last 

 whorl, upright. Inclusion one-third. 



This species is a dwarf development of the evolute form of 

 Sci'pionianum} It does not seem to show the unispinous stage 

 of that species but exhibits only a costate stage, and even further 

 decline at any early age, namely, obsolescence of the costee. In 

 fact degeneration of ornament is noticeable, while the form is small 

 as compared to Scipioniamim. 



The absence of tubercles and the small size it has attained when 

 the ribs become almost obsolete distinguish this form from Scipioni- 

 anum. The original type-specimen, which was badly figured, of 

 reduced size, in my father's work, is now in my cabinet. It came 

 from the Lias of a railway cutting at Swindon, near Cheltenham, 

 and seems to be a rare form. Unfortunately exposures of Lias in 

 the neighbourhood, or in fact in the Vale of Gloucester, are few and 

 far between now. 



P.S. — Since the above went to press I have received a pamphlet, 

 " Ueber Ammonoideen mit anormaler Wohnkammer," by Dr. J. F. 

 Pompeckj (Vereins f. Yaterl. Naterkunde in Wtirtt. 1894). This 

 may be consulted in reference to Cymbites, pp. 238-240 ; and it 

 reminds me that I have overlooked 



Cymbites centri globus (Oppel). 



Pal. Mith. p. 140, 1862, the type of which is, no doubt, the third 

 reference given under C. globosus (above). From that place may 

 be removed, to be added here, the second reference, and probably 



1 Included by authors under the name Scipioniamis, evolute and involute forms 

 may be distinguished — the former in Reynes and Wright's figures, the latter in 

 d' Orbigny's. Certainly Reynes calls his "Ammonites Scipionis,''' but this is only short 

 for Scipioniamts, d'Orbigny, whose authority he gives. Hyatt, however, dis- 

 tinguishes ^^«mcer«« Scipionianum. a^AAg. Scipionis as two species. His "Ag. 

 Scipionis'^ seems to be divisible into three: 1st, Scipionis (Eeynes), which he 

 quotes — an evolute form of Scipionianus, as alluded to above ; 2nd, Scipioniamis 

 olifex (Quenstedt, Amm. Schwab. Jura, pi. 17, figs. 7-10), which he also gives in 

 his synonomy — this seems to be a costate retrogression of Scipioniammi, and therefore 

 a cousin of Colesi, from which it differs in being more involute, more closely costate 

 to a larger size, and it probably deserves distinction as Agassiceras olifex ; 3rd, a 

 form of which an outline sketch is given in pi. 13, fig. 8 (Genesis Arietidce) — 

 a much more involute fossil than olifex, apparently very retrogressive, deserving a 

 distinct name. 



