426 THE LIAS AMMONITES. 



specimen under notice. Tlie two fragments which I have examined appear to indicate a 

 much larger total development. The reason which prevents us from attributing this fossil 

 to the vegetable kingdom is the thickness of the body, which is from two to three milli- 

 metres, and which seems to diminish on leaving the base of the fan. Ought we to regard 

 it as a fragment of the test of an unknown Ammonite of very large size ? " This extract 

 from the work of so good an observer proves the importance of having found the body- 

 chamber in sitil, thus settling the question of its true nature. During a visit I paid some 

 time ago to the Woodwardian Museum, Cambridge, I found a portion of a very large 

 fan of this shell, which was then unknown to the museum authorities. This I identified 

 and described, and it has now passed out of the unknown into the region of known fossils. 



The shell is somewhat compressed, and uncarinated, with a narrow umbilicus nearly 

 hidden. The spire is composed of very involute whorls, which almost entirely embrace 

 the preceding ones ; and the whorls, which are always oval, rounded, and compressed, have 

 their greatest width at the inner third near the spire, and they are especially wider here 

 than at the entire half of the shell. The sides of the shell and area are covered with 

 fine radiating lines which curve gently forward toAvards the aperture (PI. LXXVIII, fig. 1). 

 The size of the lines varies with the age of the shell ; in youth they are extremely narrow, 

 but in the middle-aged shells they become more and more developed. As old age advances 

 the body-chamber of this grand shell (PI. LXXVIII, fig. 1) assumes a fan-like structure, 

 in consequence of the lines being grouped into bundles of fasciculi, which radiate outwards 

 in gentle flexures from the umbilicus to the siphonal area, in elegant waved undulations, as 

 shown in our plate of this fine specimen, now in the British Museum, reduced one 

 half the natural size. It will be noted that the mould behind the suture-line is entirely 

 smooth, whilst in front of that line it develops the undulating folds which produce the fan- 

 shaped structure seen in the body-chamber of this magnificent specimen, and which I 

 believe up to this hour is quite unique. The radiating undulations appear to exist on the 

 body-chamber only inasmuch as on the moulds of the chambered portions of this fossil 

 we fail to observe those radiating depressions which constitute so important a character in 

 the body-chamber of this remarkable Cephalopod. 



The suture-line forming the lobes is extremely complicated, and formed of single parts 

 (PI. LXXVIII, fig. 2). The siphonal lobe is shorter, but as wide as the principal lateral, 

 and ornamented on each side with two branches, the inner being small, the outer much 

 ramified. The siphonal saddle is wide, and terminates in five large, oval, unequal leaves. 



The principal lateral lobe is very large, and provided on each side with three 

 ramified branches, and a long terminal branch divided into three wide foliations ; the 

 lateral saddle, longer than the siphonal, terminates in six unequal leaves, the three 

 internal leaves being smaller, whilst the three outer ones have large oval folioles which 

 make conspicuous figures on the mould ; the inner lateral lobe resembles the principal 

 lateral in structure, but is not more than two thirds the size of the principal ; the first 

 and second auxiliary saddles are formed of five folioles, the others of only three. The 



