100 JURASSIC RHYNCHONELLIDS 
specimen but it seems unlikely that it is correctly determined as, apart from its 
symmetry, the ribbing and general shape also differ from inconstans. The B.M. 
(N.H.) collection contains only one symmetrical specimen attributed to inconstans, 
a large trilobate form again from Shotover Hill. The horizon of this specimen is not 
known but, despite crushing, it is interesting in that it appears closer to Somalir- 
hynchia sutherlandi than to T. inconstans. 
While collecting material at Ringstead Bay, it was obvious that a fairly high 
proportion of the specimens obtained were unusual in that the valves “‘ gaped”’. 
The author has since examined the specimens available at the B.M.(N.H.), about 
100, and this has confirmed that about a third show this feature. Many specimens 
have a well developed epifauna and the tubes of ?Serpula are frequently seen on 
both valves. 
Torquirhynchia guebhardi (Jacob & Fallot) 
(Pl. 10, figs. 4-6, text-fig. 35) 
1913 Rhynchonella Astieriana Orbigny var. Guebhardi Jacob & Fallot: 45-46, pl. 5, fig. 9. 
1917 Rhynchonella Guebhardi Rollier: 77. 
EMENDED DIAGNOSIS. Medium-sized, globose Torquirhynchia ; markedly asym- 
metrical with a frontal notch between the two lobes ; about 30 subangular ribs ; 
radulifer crura flattened in the plane of articulation. 
STRATIGRAPHICAL RANGE. Jacob & Fallot describe it as coming from the 
“ Portlandien ’’; the author has collected it from the cymodoce zone of the Kim- 
meridgian. 
TYPE SPECIMEN. Lectotype, here selected, the specimen figured by Jacob & 
Fallot (1913), pl. 5, fig. 9 ; the type locality is St. Vallier (Alpes-Maritimes). 
MATERIAL. 7 specimens from a road cutting north of Lac d’Armaille (Ain) in 
British Museum (Nat. Hist.) nos. BB. 45762-68. Other localities in the southern 
Jura from which the species has been collected include Rossillon, Glandieu, Brognin 
Hill and Chavoley. 
DESCRIPTION. External characters. The valves are almost equally biconvex, 
with a tendency for the brachial to be slightly the more inflated. However, the 
valves are distinctively very globose and this, coupled with the very strongly 
developed asymmetry, differentiates T. guebhardi from other species in the genus. 
The beak is sharp and suberect and the shell outline subtriangular. 
T. guebhardi possesses about 30 relatively fine, subangular ribs which arise at the 
umbones and continue simply to the anterior margin ; bifurcation has only been 
observed in a few postero-laterally positioned ribs. The concentric ornament con- 
sists only of rather sparse, weak growth lamellae. 
Although the beak is quite large and suberect, the beak ridges are only weakly 
developed as are the small, incurved interareas. An oval, submesothyridid pedicle 
opening is flanked by conjunct deltidial plates. In transverse section the deltidial 
plates are clearly seen to project externally around the foramen. 
