part 1] jurassiu chronology : lias. 83 



sented by the species named by my father as Ammonites sulcatus 1 

 (now Schlotheimia sulcifera?), Schl. jiogata S. Buckman, and 

 Schl. miscella (Oppel). 3 Their date has been supposed to be 

 Amioceras (Lymian 7) ; but, as they do not occur in other areas 

 where the Amioceras fauna is common, it may be suggested that 

 strict contemporaneity is doubtful, and again two faunal horizons 

 .are possible. They have been found only in a very limited area : 

 which does not mean that their dispersal was at fault, because the 

 explanation is possibly strata! failure — their deposits destroyed by 

 ■one of the many Jurassic erosions. Gloucestershire is the only 

 locality for the forms above mentioned, 4 but what I adjudge 

 as similar, possibly contemporaneous forms, though not identical 

 species, are some of these small Schlotheimia from the Lias of 

 Spezia (Italy), 5 Schl. lacunoides of Wiirtemberg, Schl. coinpta, 

 Schl. ventricosa (Sowerby, Canavari), Schl. cf. lacunoides (Quen- 

 stedt) quoted from Yorkshire, 7 and those specimens which 

 Dumortier calls, I presume incorrectly, Ammonites lacunatus 

 .and places below the stellare horizon (Mercian 6). His figured 

 A. lacunatus (Schl. deleta Canavari) belongs to the next wave. 



This third wave of Schhtheimice consists of a very considerable 

 number of quite small, generally fine-ribbed species, of which 

 A. lacunatus J. Buckman is the most quoted example, the date 

 •of which, now under consideration, is with or later than denotatus 

 (Mercian 7), but -pre- G-agaticeras (Deiran 1). These species 

 occur over a considerable area of Europe : for A. (Schlotheimia) 

 lacunatus has been claimed, though not always quite correctly 

 identified, for Italy, Hierlatz, Wiirtemberg, the Rhone Basin, and 

 England (Gloucestershire) ; and with allied species, one identified 

 with a Hierlatz species, the range extends to Yorkshire. It is this 

 range which is the subject of the subjoined Table VIII (p. 84), 

 together with that of involute Arietites of denotatus pattern. 



The first point to be noticed in this analysis is that the Schlot- 

 heimia of the third wave occur in Italy, at Hierlatz, and at 

 Gloucester — localities which show no Arietites indicative of 

 denotatus (Mercian 7), and that they do occur in Wiirtemberg, at 

 Cheltenham, and in Yorkshire — localities which do show Arietites. 

 The absence of Arietites from certain places is the point to explain. 

 Italy and Hierlatz, it might be urged, are beyond the range of 

 these Arietites ; and, for Gloucester, collection failure might be put 

 forward, as already remarked. But Quenstedt supplies evidence 

 that there are two horizons — one of Arietites and one of lacunatus, 



1 II, 2, No. 39. 2 II, 4, p. 38 b. 3 II, 2, No. 39, note. 



4 The strata from this horizon in Gloucestershire suffer from exposure 

 failure : they have not been properly uncovered since the making' of the 

 Bristol-Birmingham Railway in the 'forties. 



5 Two of these Spezia species are said to come from the marmorea and 

 rotiformis zones of the North-Eastern Alps (XXII, pi. xxi, fig - . 6, & pi. xxii, 

 figs. 1-2), but the identifications do not seem quite satisfactory. 



6 II, 3, pp. 240, 241. 



7 II, 6, p. 99 : entered with the third wave ; but it may be earlier. 



g2 



