GRAMMOCERAS MUELLERI. 209 



Geammocekas MuellePvI {Denchmann). Plate XXXIV, figs. 8, 9 ; Plate XXXV, 



figs. 1—3. 



1887. Ammonites (Haepoceeas) Muelleei, Benclcmann. Fauua von Dornteu ; 



Abh. der geol. Specialkarte v. 

 Preussen, &c., Bd. viii, Heft 2, pi. 

 iii, fig. 3 ; pi. iv, fig. 2 ; pi. x, fig. 8. 



Discoiclal, compressed, hollo w-carinate. Whorls with broad, nearly parallel 

 sides, ornamented with subarcuate radii. Ventral area undefined, scored by the 

 ventrally-projected radii, and carrying a large hollow carina. Inner margin well 

 marked, smooth, sloping, convex. Inclusion about one-third. Umbilicus fairly 

 open, somewhat depressed, increasing in size slowly. 



In general appearance this form approaches Gramm. suhquadratum, but may be 

 at once distinguished from it by broader whorls, straighter ribbing, greater com- 

 pression, and a more closed umbilicus. We may consider this form to be derived 

 from Gramm. suhquadratum, and that we have an " ascending series " — Gramm. 

 quadratum, Gramm. suhquadratum, Gramm. Muelleri. 



From Gramm. fallaciosum the slower coiling and the distinct inner margin 

 easily separate it. 



In many respects this form converges to Haufjia occidentalis, but may be 

 distinguished by greater thickness, a smaller umbilicus, and more conspicuous 

 ribs. Young specimens, in which the ribs are well preserved, are easily separable 

 on account of the stronger ventral projection thereof; but in older specimens this 

 feature is not so conspicuous — in fact, the whorl becomes altogether nearly smooth ; 

 and, in the case of poorly preserved specimens, there is a great simulation of 

 Haugia, 



Denckmann's figures of this species represent only small forms. My figures 

 1 and 2 in PL XXXV, show what is probably an adult example. Denckmann speaks 

 of indications of furrows upon the ventral area (Andeutung von Furchen) ; but I 

 cannot detect this in my specimens. Doubtless very small examples possess this 

 character, since indications of small furrows can be detected at the end of the 

 whorl in Gh'amm. suhquadratum. The small specimen which I have had depicted 

 has irregular ribs slightly bunched on the inner area ; while the edge of the inner 

 area of the older specimens is uneven, probably from the same cause. 



Gi'amm. Muelleri is a very scarce form. It occurs with Gramm. fallaciosum, 

 &c., in the Disponsum-hQ^iQ, and I have collected it at Stinchcombe, North Nibley, 

 and Sodbury, Gloucestershire. None of the examples possess any test. PL 

 XXXV, figs. 1, 2, give two views of a large specimen; fig. 2 shows the partition- 



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