78 
JURASSIC^ OR 
AMMONITES TENUISTRIATUS.-O^y. 
[Plate 14; fig. 2?] PL 15; fig. 2. 
A. tenuisulcatus, Gray. Hardwicke’s Illustrations, vol. i., pi. 100, 
fig. 4. 
A. testa discoidea, compressa, umbilicata, crcbricostata. Anfrac- 
tibus latis, complanatis; ventre rotundato. Costis ilexuosis, per 
medium anfractus bifurcatis, apud ventrem antroi’sum acute arcuatis. 
Apertura oblonga. 
Diameter ... ... ... 3'35 in, Spiral ratio... 
Ditto of outer whorl ... D4 „ Immersion of wliorls 
Thickness... ... ... 0'9 „ Thickness : diameter 
Nearly allied to A. JSFepalensis , Gray; of wliicli; indeed; I am 
inclined to think it is only a variety. It is more compressed 
and flattened than that species; has a somewhat larger um¬ 
bilicus; and more numerous and finer ribs (about twice as 
many in the two specimens examined; one of which is Hard¬ 
wicke’s type). The curvature of the ribs is similar in the 
two species; except that the ventral arcuation is rather more 
acute in A. termistriatus. The sutures are not visible. 
AMMONITES UMBO .-Stracliei,, MSS. 
Plate 17; fig. 2. 
A. testa discoidea, late umbilicata. Anfractibus depressis, rotun- 
datis, costatis, per medium serie unica tuberculis permagnis 
ornatis. Costis simplicibus, rotundatis,—nonnullis apud umbilieum, 
aliis apud tuberculos orientibus : in margine sub-interruptis. Aper¬ 
tura reniformi. 
Diameter of fragmentary whorl 1 7 in. Spiral ratio . 2:1 
Thickness ... ... ... 2*1 „ Immersion of whorls ... T y 
Thickness : diameter ... i 
6 
An Ammonite of the A. anceps and A. coronatus type, 
ornamented with a series of large bossy tubercles on the mid¬ 
dle of the whorl, and well-developed, rounded ribs, which are 
slightly interrupted over the siphuncle. The sutures bear 
much general resemblance to those of A. ancejjs, but differ in 
the details, having an additional auxiliary lobe, and a nar¬ 
rower ventral, and broader lateral saddles. 
2 : 1 
5 
3 _ 
5 
