﻿236 INFERIOR OOLITE AMMONITES. 



Chief among the literature dealing with Dumortieria and its ally Catulloceras I 

 must mention Haug's excellent work, " Ueber die Pohjmorphidae, eine neue 

 Ammonitenfamilie aus dem Lias," ' Neues Jahrbuch fiir Mineralogie, &c.,' Beil.-Bd. 

 ii, 1887. Commencing with the Lower Lias, it treats of Agasslceras and different 

 branches which have sprung therefrom (including Dumortieria) in a very complete 

 manner. Its two plates contain figures of certain new species of the genus ; and 

 numerous tracings of suture-lines are given in the text. Another work to be con- 

 sulted is Branco's ' Untere Dogger;' but see p. 169. 



Dumortieria prisca, 1 S. Buchman. Plate XXXVII, figs. 9 — 11. 



Discoidal, evolute, carinate. Whorls almost circular, ornamented with coarse, 

 distant, irregularly placed, direct ribs, which become smaller and closer-set on the 

 last. Ventral area not defined, convex, divided by a very small carina, which is 

 met almost at right angles by extremely obscure ribs. No inner margin. Inclu- 

 sion about one-third or less. Umbilicus open, with gibbous-sided whorls orna- 

 mented with coarse, unequal-sized, unequally placed, distant ribs. Suture-line with 

 a well-marked superior lateral lobe, and a markedly dependent inner portion. 



The form, the ornamentation, and the sutures of this species are extremely 

 suggestive of Caloceras (Ophioceras), especially of such a species as Cal. liassicum. 

 These characteristics indicate that this is a little-developed form — that, in fact, 

 this species from the Jurense-zone has only attained the same stage of development 

 as these species of Caloceras at the base of the Lower Lias. The development of 

 the ancestors of this species must have been greatly retarded ; and it is not a little 

 singular that when they did develop they should so copy the Lower-Liassic 

 derivations from the ancestral stock {Caloceras). It is on account of this likeness to 

 an ancient form that I have given this species the name of " priscus," old-fashioned. 



Of course this species is the ancestor of Bum. Levesquei. Its outer whorl, 

 where the ribs become smaller and closer-set, comparatively, and which has a 

 slightly less circular section than its predecessors, foreshadows the features which 

 are peculiar to Bum. Levesquei; and just in the same manner the outer whorls of 

 Bum. Levesquei foreshadow the features which are peculiar and much more deve- 

 loped in Bum. striatulocostata, Bum. pseudoradiosa, or Bum. radians. 



I believe that this species is undescribed. It is most interesting as supplying 

 a link in the genealogy of Bum. Levesquei; and it indicates whence are derived 

 those coarse irregular ribs to be seen in the innermost whorls of all species of 

 Bumortieria, unless obliterated by the encroachment of senility. 



1 " Priscus" = old-fashioned. 



