W. B. Clark — Ammonite from the Alpine jRhwtic heels. 119 



"When we examine the stratigraphical relation of these beds 

 to the underlying Trias we find that no unconformity exists, 

 but that an insensible gradation often takes place from one to 

 the other ; while toward the Lias, on the other hand, although 

 unconformity does not exist, yet the break is so marked and 

 clearly defined that we are unprepared to admit an intimate 

 connection between the Rheetic and Lias. 



Stratigraphical and paleontological evidence in the Eastern 

 Alps is, -then, strongly indicative of a close affinity of the 

 Ehsetic to "Trias ; and the Arcestes species, which we will now 

 describe more in detail, adds another important proof to this 

 more or less generally accepted fact. 



Arcestes ehaeticus, n. sp.* 



The ammonite in question, to which, from its important oc- 

 currence, I have given the name of Arcestes rhceticus, has the 

 following dimensions : 



Diameter 70 mm 



Height of last whorl 40 



Thickuess 50 



Umbilicus 14 



The shell is involute, with rounded dorsal surface, and the 

 cast shows upon the last whorl two depressions, which run 

 in a straight line over the convex back, and which were occa- 

 sioned by successive contractions or interior thickenings of 

 earlier mouth-edges. The sutures form regularly decreasing 

 series of lobes and saddles from the dorsal siphuncle toward the 

 interior. These lobes and saddles are finely branched, the lat- 

 ter containing upon the outside 4-5, upon the inside 3 ob- 

 liquely diverging divisions. Beyond the dorsal and the two 

 lateral saddles there are only two auxiliary saddles present. 

 The dorsal lobe is divided by a median saddle into two points, 

 which are very considerably deeper than the lateral lobes. The 

 latter are by means of small branches two- or three-pointed. 



This species belongs to the group of the Galeati, and shows 

 close affinities to Arcestes giganto-galeatus Mojs., from the 

 Hallstadter Kalk. 



We have thus a form which belongs to a family and genus 

 most characteristic for the Trias and until now never found 

 above that formation. The Lias has not a single representa- 

 tive. The interest in this particular species is greatly height- 

 ened from the very close similarity in outward form and mi- 

 nute division of the lobes to Arcestes giganto-galeatus. This 

 fact, if we were to consider the Ehsetic beds as belonging to 

 the Lias, would be without a parallel, for on account of the ex- 



* Figured iu the paper before mentioned, Plate I, fig. 3, a, b, c. 



