68 JURASSIC RHYNCHONELLIDS 
a wide range in the size of the individuals and as they are very well preserved this 
would indicate that they had not been carried far, if at all, before being buried. 
A. (Acanthorhynchia) spinulosa (Oppel) 
(Pl. 6, figs. 8-9, text-fig. 25 (top)) 
1850 Hemithiris senticosa (pars) Orbigny: 375. 
1857 Rhynchonella spinulosa (pars) Oppel: 608. 
1904 <Acanthothyris spinulosa (Oppel); Loriol: 284-85, pl. 27, fig. 44. 
1917. Acanthothyris spinulosa (Oppel); Rollier: 79. 
EMENDED DIAGNOSIS. Medium sized Acanthorhynchia ; transversely oval in out- 
line ; anterior commissure rectimarginate or with very slight uniplication ; beak 
small and incurved ; beak ridges and interarea present. 
STRATIGRAPHICAL RANGE. Oxfordian—exact horizons not known. 
TYPE SPECIMEN. A type specimen is not selected as this would have to be chosen 
from Orbigny’s specimens of Hemithiris spinulosa (discussed below) and these are 
neither stratigraphically nor geographically accurately located. 
MATERIAL. 2 specimens, collection of University of Dijon from Mt. Saon (Haute 
Marne) France ; 6 specimens, collection of B.M.(N.H.) nos. B. 70044—49, from 
Haute Marne ; 2 specimens Orbigny collection. 
DeEscriPTION. External characters. The shell is equally biconvex and the width 
is greater than the length. The thin test is evenly covered with fine bifurcating ribs 
bearing numerous spine bases along their crests. The ribs are coarser and the spine 
bases more widely spaced than in A. (Acanthorhynchia) panacanthina. 
Beak ridges are developed and limit the small but distinct interarea ; the small, 
incurved beak is adpressed to the brachial valve and obscures the delthyrium. 
Deltidial plates are disjunct and only weakly developed ; they appear briefly in a 
few of the anterior serial sections. Weakly developed growth lamellae, but not 
growth lines, may be present. 
DIMENSIONS OF FIGURED SPECIMENS. 
length thickness width 
2°30 cm I-40 cm 2°54 cm 
2°05 cm I'Io cm 2°35 cm 
Internal characters. Pedicle valve. Dental lamellae are completely lacking and 
the teeth are inserted laterally at a rather shallow angle. 
Brachial valve. The most distinctive internal feature is the presence of what 
appears to be a cardinal process, developed from the inner hinge plates. The long, 
straight sockets, as seen in section 1-9 of text-fig. 25 appear to be distinctive. The 
crura are radulifer and curve slightly towards the pedicle valve. The median septum 
is poorly developed and is present only as a median ridge for most of its length. 
DIsTRIBUTION. The only records are from the Haute Marne area of France and 
from the Ledonien Jura. 
REMARKS. The name sPinulosa was first used by Oppel (1857) when he cited it 
as a ‘“‘new name” for Hemithiris senticosa Orbigny in a list of Oxfordian fossils ; 
unfortunately, he did not figure or state exactly what he meant by it. 
