Geological Society. 241 



Midlands, while at the same time showing the various non-sequences 

 in both areas. 



Some critical palaeontological remarks are made concerning the 

 identification of certain species of ammonites, and a correction of 

 nomenclature is made, with a new name for a species misidentified 

 on account of homoeomorphy. This leads to a few remarks on 

 development and homceomorphy, wherein an important difference 

 in the mode of development of certain Kelloway Kock-Oxford Clay 

 genera is pointed out, and it is remarked that there are three 

 methods of homceomorphy — (1) subparallel, the likeness of stocks 

 passing through similar stages ; (2) transversal, the likeness of 

 stocks starting from different forms meeting at a cross-over or 

 collision-point ; and (3) cyclical, the likeness of an anagenetic 

 to a catagenetic series. 



2. ' On Jurassic Ammonites from Jebel Zaghuan (Tunis).' By 

 Leonard Frank Spath, B.Sc, F.G.S. 



Jebel Zaghuan, the best-known and most conspicuous, though not 

 the highest, mountain of the Tunisian Atlas, is built up largely of 

 massive bluish-grey limestones of confused stratification which have 

 been referred to the Middle Lias on the evidence of badly-preserved 

 belemnites and Terehratulce, notably 'P//r/o/>e' astasia, Columna sp. 

 Middle Liassic (Domerian) ammonites are now recorded for the 

 first time. A new classification of the Domerian genera of the 

 family Hildoceratidae, to which the fossils from Jebel Zaghuan 

 belong, is proposed. 



Moreover the ammonites collected by the Author afford sufficient 

 evidence of the presence of the zone of Heineckia ance^s, which 

 occurs in Algeria, but had been supposed absent in Tunis together 

 with the other beds intervening between the Middle Lias and the 

 Corallian. The Middle Jurassic transgression must, therefore, have 

 begun in Lower Oxfordian times, since the deposits of that age 

 probably rest directly on the Domerian. 



The upper zones of the Oxfordian, as well as the lower part of 

 the Corallian as interpreted by Mr. Buckman : that is, the cordatus 

 and iive-cor</a(vs zones, seem to be absent, although there is a possi- 

 bilit y t hat they have been cut out by the extensive faulting, of which 

 the general calamitization seems to afford proof. 



On the other hand, the Argovian, or zone of Peltoceras trans- 

 versarium, is very well represented. About seventy specimens were 

 collected at a locality called Sidi Bu Gubn'n, but the list includes 

 forms from the transversarius zone mixed with some from the 

 ' acanihicus ' beds, If we call to mind the curious fact that, not 

 only in the Southern Alps, but also in Sicily the Argovian is very 

 well developed, to the exclusion of the higher beds of the Corallian, 

 followed without any apparent break by the ' acantkicus' beds, it 

 appears quite probable that the two ' zones ' occur here in a similar 

 manner, and that the apparent mixture is not due to doubtful 

 identifications of badly-preserved specimens. 



Ann. <!• Mag. N. Hist. Ser. 8. Vol. xii. 17 



