382 THE LIAS AMMONITES. 



Koclilin Schlumberger^ has, through a series of strict investigation of a quantity of mate- 

 rial from Mende, Lozere, and Venarey, Cote d'Or, arrived at the conclusion that Am. 

 Henleyi and Am. Bechei, as figured by d'Orbigny, do not belong to two different species, 

 but constitute only varieties which, through transition forms, are completely united into 

 one species. The two forms are bracketed together in the works of Quenstedt, Oppel, 

 Dumortier, and by Professors Tate and Blake in their Yorkshire Lias. Still, not- 

 withstanding these authorities, the fact remains that the two species lie close together 

 in the same bed on the Dorsetshire Coast, without any transition forms uniting them. 



Locality and Stratigraphical Position. — This Ammonite is found in the Upper INIarls 

 without mica, near Charmouth, Dorset, in which many specimens are found associated with 

 Lytoceras fimhriatum^ Aegoceras striatum^ Phylloceras Loscombi, Nautilus semisiriatus, 

 &c. I have found a specimen in the Green Ammonite Bed of the same section above 

 the marls in company with Aey. Davcei and Monotis inaquivalvis. It likewise has 

 been collected from the Middle Lias at Eenny Compton, Warwickshire, and in 

 Northamptonshire, as well as in Robin Hood's Bay, Yorkshire, from the zone of Aey. 

 capricornus-==.Aeg . Henleyi. 



Foreign Distribution. — In France it has been collected in the Middle Lias below the 

 beds with Gryplicea cymbium at Saint-Rambert, Ain ; at Courtards, near Saint-Amand, 

 Cher ; at Eresnay-le-Puceux, at Curcy, at Vieux-Pont, Calvados ; at Semur and Venarey, 

 Cote-d'Or ; and Avallon, Yonne, by several distinguished palaeontologists. Professor 

 Quenstedt says Sowerby makes two species, Am. Bechei and Am. Henleyi, out of Am. 

 striatus, observing " Am. Bechei, with its rounded back, finer ribs, smaller tubercles, and 

 more rapid increase in thickness, is very often found in Wiirtemburg. Whilst Am. 

 Henleyi, with its hexagonal mouth-opening, larger ribs, stronger tubercles, slower increase 

 in thickness, and indistinct longitudinal striae, lies deeper, and in Wiirtemberg is more 

 rare." ' Cephalopoden,' p. 135. 



.— ARCESTIDiE,' Mojsisovics, 1875. 



This interesting family, containing the genera Arcestes, Didymites, Lobites, Ptychites, 

 Pinacoceras, Sageceras, Amaltheus and Schhenbacliia, and comprising for the most part 

 the first Ammonites that appeared in the Trias seas, has the ancient genus Arcestes, Suess, 

 as its type. The shell is usually more or less globose, or has largely inflated sides, occa- 

 sionally it is compressed and carinated ; it is either smooth, or possesses an ornate surface, 

 formed of transverse folds, costa3, or fine longitudinal striations. The lobe-line in 

 Arcestes is very complicated and formed of many divisions, each having a central stem 

 with short, transverse, and oblique digitations, the whole constituting most intricate folia- 



1 'Bullet. Soc. Geol. de France,' Juin, 1854, p. G28. 

 - See page 238 of this Monograph. 



