ARIETITES BONNARDII. 287 



whence I obtained a series of specimens in different stages of development, and where it 

 is associated with A. Turneri and A. Bonnardii. It is found in the upper part of the zone 

 of A. Bucldandi, Robin Hood's Bay, Redcar, Marske, Nunthorpe, Ellerbeck ; and 

 zone of Amal. oxgnotus, Robin Hood's Bay, Yorkshire, and in the Lower Lias Shales 

 and Limestones at Bredon, Lansdovvn, Cheltenham, and other places in the Vale of 

 Gloucester. 



Foreign Distribution. — In North Germany at Scheppau, Achim, Stadtoldendorf, 

 Bundheim am Harz, Langelsheim am Harz, Brunswick; Salzgitter (Haverlah-Wiese), 

 Hullersen and Wellersen, Hanover; and in many other localities. 



In South Germany at Gniiind, Krummenacker, Goppingen, and Bebenhausen, near 

 Tubingen. 



Arietites Bonnardii, d'Orbigng. PI. XI, figs. 1, 2, 3. 



Ammonites Bonnardii, cFOrbigny. Paleont. Fran9., Terr. Jurass., p. 196, pi. xlvi, 

 1842. 



Diagnosis.' — Shell discoidal ; sides much compressed and ornamented with numerous 

 (forty) ribs, which first arch backwards, then incline forwards, and finally bend round the 

 margin, inclining obliquely forwards, and vanishing at the outer side of the sulcus. 

 Siphonal area with a medium-sized keel between two deep lateral sulci. Aperture rectan- 

 gular, subquadrate, compressed at the sides. 



Dimensions. — Transverse diameter of the figured specimen, 110 millimetres ; height 

 of the last whorl, 25 millimetres ; thickness of ditto, 22 millimetres. Amount of 

 involution, 3 millimetres. 



Description. — Shell discoidal, much depressed, carinated, and sulcated ; whorls 

 numerous (eight). The sides ornamented with forty ribs, mostly simple, rarely bifurcate, 

 much arched, and rounded. The siphonal area broad, provided with a medium-sized 

 prominent keel, having on each side a deep sulcus. The spire is composed of narrow 

 compressed whorls, with very regular ribbing. 



The aperture is rectangular, subquadrate, and compressed at the sides, with a promi- 

 nent ventral process. The lobe-line is not shown on any of my specimens. D'Orbigny 1 

 describes the siphonal lobe as a little larger, and quite as long as the principal lateral, 

 and ornamented with many conical digitations. The siphonal saddle is twice the size of the 

 principal lateral lobe, and is divided into four round unequal leaves by three lobules, of 

 which the central one has nine digitations. The principal lateral lobe is ornamented on each 

 side with three branches, which increase in length from above downwards. The first has 

 two digitations, the second three, and the third six ; and the external branch is longer than 

 the other. The lateral saddle, narrower than the principal lateral lobe, is unequally parted 

 1 ' Paleontologie Francaise, ter. Jur.,' tome i, p. 196, pi. xlvi, fig. 3, 1842. 



