GRAMMOCERAS QUADRATUM. 201 



I have alluded above to the similarity of ribbing in the " Fallaciosum-grou^.^' 

 Well-preserved examples have an appearance, not as if they were ribbed, but as if 

 sulcated, and that the sulci had been cut out with a gouge held slightly aslant 

 towards the preceding rib, and as if the lower corner of the gouge had cut a 

 ribbon from out of the side of that rib. This appearance may be explained as 

 follows : — The top of the ribs is more or less flattened, especially so in Gramm. 

 Struckmanni ; between the ribs, and about equal to them in breadth, is a concave 

 furrow, interrupted about the middle, or towards the previous rib, by a small, 

 raised, thread-like line. I cannot detect this kind of ribbing on Gramm. metal- 

 larium ; while Gramm. dispansicm is never well enough preserved. 



It may be worth noting that the only way to obtain good specimens of 

 Ammonites of the " Fallaciosum-growY) " in the Cotteswolds — and they occur 

 hardly anywhere else — is to employ a man to make an opening on purpose. Then 

 the matrix must be entirely removed from the specimens out in the field while 

 they are still wet ; otherwise it adheres tenaciously, and the result is generally 

 very unsatisfactory. 



Grammoceeas quadeatum (Hang). Plate XXXIV, figs. 6, 7. 



1846. Ammonites eadians quadeatus, Quenstedt. Cephalopoden, p. 113. 

 1874. — QiLV:>!Oyfi, Bumortier {non Sauer). Etudes pal. Bassin Eh one, 



iv, pi. xiv, figs. 6, 7 ; pi. xv, figs. 1, 2. 

 1855. HiLDocEBAS QUADEATUM, Httug. Beitr. Monogr. Harpoceras; Neues Jabr- 



buch fiir Mineral., &c., Beil.-Band iii, 



p. 638. 



Discoidal, presumably hollow-carinate. Whorls quadrate, ornamented with 

 coarse, subarcuate ribs. Ventral area broad, carrying a prominent carina, on each 

 side of which is a shallow sulcus. Inclusion slight. 



This is really a very distinct form ; but, since I possess very insufficient 

 material, I have only been able to figure a young specimen. A capital figure 

 of this species is given by Dumortier (see synonyms) under the incorrect name 

 Am. Grunoioi, Hauer.^ Haug, referring to Dumortier's figure, gave to this form 

 the name Hildoceras quadratum, presuming that it was the form to which 

 Quenstedt alluded under the name Am. radians quadratus, ' Ceph,' p. 113. To 

 include it in the genus Hildoceras was, however, not correct (p. 160). Its 

 ribbing is typical of Grammoceras, and it is probably the parent of Gramm. 

 Sasmanni, fallaciosum, &c. 



1 A totally different species ; belongs to Am. liassicus-gTOUip (Ophioceras) . 



26 



