﻿240 INFERIOR OOLITE AMMONITES. 



the centre than outside, ornamented with coarse, rounded, unequal-sized, irregu- 

 larly distant ribs. Suture-line with rather short superior lateral lobe. 



Only one specimen is known to me, but it agrees exactly with Hang's delinea- 

 tions except in the matter of the suture-line. This is not quite characteristic of 

 the genus ; it has shorter lobes and a less dependent inner portion than in Haug's 

 drawing, and therefore appears more like the suture-line of a Gn'amm,oceras. These 

 discrepancies, however, may possibly be explained by the fact that the sutures visible 

 on my specimen are the last three ; and, as they exhibit a decided reduction — the 

 last being simpler than the penultimate, and this again than the antepenultimate, 

 it is possible to infer that perhaps at half a whorl further back the suture-line would 

 agree with Haug's delineation, which shows a characteristic Dumortieria-\obe-\me. 



Another point about this species which makes it resemble Grammoceras is the 

 slight bending of the ribbing on the lateral area. It lacks, however, the strong 

 forward ventral bend of Grammoceras. The ribs, it is true, disappear on the outer 

 area, but their direction may be seen by following the fine growth-lines visible on 

 the crystalline test. 



Analogy, too, points strongly to the fact that my specimen is a Dumortieria, 

 and is correctly identified, therefore, with Haug's species. Its inner whorls 

 (diameter about 1 2 lines) conform so exactly in appearance with Dumortieria prisca 

 (reaching 21 lines) — the same coarse irregular ribs are seen in the inner whorls of 

 both species, only that they are not continued so long a time in Bum. sparsicosta. 



A generally greater compression, and a sharper, more carinate ventral area, 

 easily distinguish Dum. sparsicosta from Bum. prisca, its ancestor ; while an umbi- 

 licus slightly more slowly-coiled, a whorl less gibbous ventrally, and numerous 

 differences of ribbing distinguish it from its " cousin," Dum. costula. The 

 characters of its ribs separate it completely from Dum. Levesquei. 



Under the name "falcofila sparsicosta" Quenstedt figured two species in his 

 ' Schwab. Amm.' One (fig. 35) is Dum. costula; the other (fig. 29) is a small 

 specimen, and might be the young of several species of Dumortieria, as, for 

 instance, of Dum. prisca, Dum. costula, Dum. Levesquei, Dum. striatulo-costata, or 

 this species. Haug having given a good figure and description of the present 

 species under the present name, I consider Dum. sparsicosta to be founded on his 

 authority, and that Quenstedt's figures may be left out of account altogether. 



Only one specimen of this easily recognisable species have I had the good 

 fortune to meet with. It came from the ilfoom'-beds (Opalinum-zone) of Buckholt 

 Wood, and, for a Cotteswold specimen, is in very good preservation. 



PI. XLV, figs. 17, 18, exhibit two views of the above-mentioned specimen. 

 Fig. 19 illustrates the aperture, and fig. 20 shows the penultimate and antepenulti- 

 mate suture-lines from the same fossil. 



