﻿244 INFERIOR OOLITE AMMONITES. 



so curiously alike ; and when the gibbous inner whorls are covered by the flattened 

 outer whorls the whole appearance of the species is changed. 



The adult specimen, PI. XL, figs. 1, 2, illustrates this matter exactly. Appa- 

 rently it differs but little from Grammoceras doemtense (PI. XXIX, figs. 1, 2) or 

 from Gramm. aalense (PI. XXXII, figs. 1, 2) ; but its young (PL XL, tigs. 3 — 6) 

 differs very appreciably from the young of either Gramm. doemtense (PI. XXIX, 

 figs. 6, 7) or Gramm. aalense (PI. XXXII, fig. 3). 



Dumortieria striatulo-costata is evidently a further development of Bum. 

 Levesquei. Practically speaking, its inner whorls (PI. XL, figs. 3, 4) are Dum. 

 Levesquei in miniature ; and it is not until it has passed a diameter of 10 lines that 

 the specific characters peculiar to D. striatulo-costata are developed. 



Under the name striatulo-costatus, Quenstedt combined a series of four species, 

 as Dr. Haug has already noticed. 1 For Quenstedt's fig. 7 alone Haug retained the 

 name " striatulo-costatus ;" but he reserved it as a variety of Branco's " subundu- 

 latus." I agree with Dr. Haug as to the form to which the name striatulo-costatus 

 shall be applied, though I extend its range somewhat to include certain others, and 

 give it specific rank ; but for certain reasons (see article on Dum. subundulata) I 

 reserve Branco's name " subundulata " for his pi. iii, fig. 4. 



Of the present species there are several varieties illustrating a gradual change 

 of form due to development in the normal manner. First there is Quenstedt's 

 wide-centred form, which retains the ancestral — the Levesquei — stage to a late 

 period of growth. Of this I have only poor examples, not good enough to figure. 

 Next there is the form figured by Branco (his pi. iii, fig. 3 only) and by Haug 

 (" Polymorphidge," pi. v, fig. 4), each of which has a smaller centre than Quen- 

 stedt's. I have not a specimen sufficiently good for delineation ; but they only 

 differ from those I have had depicted (PI. XL, figs. 1 — 9) and from Haug's figures 

 of subundulatum (' Nouv. Amm.,' pi. xiii, fig. 2) in not being so much pinched 

 ventrally. I doubt if it be worth while to distinguish between these two forms. 

 I fancy they may be united as var. « ; while var. /3 differs in being much more 

 compressed, and in losing the Levesquei-st&ge at a very much Earlier age. Var. /3 

 is illustrated by two slightly different forms — one a south-country specimen, PL 

 XXXVII, figs. 16, 17 ; the other a Cotteswold specimen, PL XL, figs. 10—12. 



Taken altogether, the whole series indicates gradual development from the 

 evolute ancestor Dum. Levesquei to the more involute, compressed Dum. striatulo- 

 costata, var. (5, and this series is parallel to the Levesquei-Moorei series (p. 242). 



To return to the species figured by Quenstedt under the name " striatulo- 

 costalus.'' His fig. 7, as I have said, may be taken as the type of the present species; 

 fig. 8 is Dum. costula (p. 237) ; to the form depicted in fig. 9 Haug has given the 



1 " Polymorphic^," ' Neues Jahrbucb fiir Mineralogie, &c.,' Bd. ii, p. 135, 1887. 



