﻿DUMORTIERIA STRIATULO-COSTATA. 243 



Dumortieria striatulo-costata, Quenstedt. Plate XXXVII, figs. 16 and 17 ; 



Plate XL, figs. 1—12. 



1879. Harpoceeas subundulatum, varietat exteene-costatum, Branco. Unt. 



Dogger; Abh. geol. Spez.-Karte Elsass- 

 Lothringen, Bd. ii, pi. iii, fig. 3 only 

 {not 4, 5). 



1884. — Haug. Nouvelles Amm. Lias sup. ; Bull. 



Soc. Geol. France, 3e ser., t. xii, pi. xiii, 

 fig. 2. 



1885. — — var. exteene-costatum, Haug. Beitr. 



Monogr. Harpoc. ; Neues Jabrbucb. fur 

 Mineralogie, &c, Beil.-Bd. iii, p. 663 (pars). 



1885. Ammonites steiatulo-costatus, Quenstedt. Amm. Sehwabischen Jura, 



pi. Iii, fig. 7 only {not 8, 9, 10). 



1887. Dumoetiebia subundulata, varietat steiatulo-costata, Haug. " Poly- 



morpbidae ;" Neues Jahrbuch fur Mine- 

 ralogie, <&c., Bd. ii, p. 135, pi. v, fig. 4. 



Adult : Discoidal, compressed, carinate. Whorls flattened, ornamented with 

 subdirect, ventrally-inclined ribs. Ventral area narrow, ornamented with a small, 

 distinct carina. Inner margin convex, but scarcely defined. Inclusion about one- 

 half. Umbilicus open, rather flat, and scored with straight, distant ribs. 



Immature : Up to a diameter of about 9 lines the whorls are strongly gibbous, 

 scarcely carinate, and ornamented with direct ribs strongly marked on the lateral 

 area, slightly inclined but inconspicuous on the ventral area. Ventral area 

 almost smooth, convex, slightly carinate. 



What Haug calls the polymorphism of this species is rather remarkable. The 

 Ophioceratan- or Caloceratan-like form lasts until the example is about 9 or 10 lines 

 in diameter (PI. XL, figs. 3, 4). In about another half- whorl a complete change 

 takes place — the Grammoceratan-like form is assumed — the gibbous whorl becomes 

 flattened, the convex ventral area becomes pinched and sharpened, the almost 

 circular aperture becomes elliptical (PI. XL, figs. 5, 6). A still greater progress 

 of the Grammoceratan-like character is shown in another half- whorl, and conse- 

 quently there is an extraordinary difference in the features of this and of the 

 preceding whorl. I have had figs. 3 — 8 in PL XL expressly arranged to illustrate 

 these changes. All the figures are taken from one specimen which was broken up 

 so as to show the inner whorls ; and fig. 7 is a correct view of this specimen when 

 joined together. These changes are important, because, while the inner whorls 

 are so totally different from the inner whorls of Grammoceras, the outer whorls are 



