440 THE LIAS AMMONITES. 



PI. LX has a singular history. One half of this specimen was discovered at Grettan, 

 Gloucestershire, a long time ago, in the turning over of a heap of rubbish, from whence 

 it came into my hands. I found the inner costated whorls of its early condition very 

 well displayed in the fragment, and a portion of its adult state as well. I promised my 

 collector a good fee if he would find the rest of the fossil, which I was certain, from the 

 fractured surface, remained in the heap ; after a two days' search a second fragment was 

 found, which when placed in position still left a gap. Again I renewed my promise, and 

 another long search over the stuff disclosed the third missing fragment. Soaking the 

 mutilated specimen in boiling water I detached all the fragments, and having cleaned their 

 fractured surfaces, cemented them together and produced the fine Marpoceras Levisoni 

 figured in PL LX. The shell is converted into crystallised carbonate of lime, which 

 completely conceals the mould and much of the suture-line; this line, however, is shown 

 in the young ribbed shell (PI. LXI, fig. 3). 



The siphonal lobe is long, the sides present several digitations, and it terminates in a 

 long divergent branch. The siphonal saddle is twice the width of the lobe, it has an 

 accessory lobule arising in the middle, and dividing the space into two compartments^ 

 which terminate in many shallow folioles. The principal lateral lobe is a large mass 

 with four or five lateral digitations, and a round head surmounted by four digitations 

 (PI. LX, fig. 1, and PI. LXI, fig. 3). The lateral saddle is smaller than the siphonal, it 

 is unequal in form, inclines towards the principal lobe, and terminates in five or six 

 shallow, obtuse folioles. The inner lateral lobe is much smaller than the principal, it has 

 several lateral digitations, and a terminal lanceolate one. The auxiUary lobes and saddles 

 were small and imperfectly shown in the specimen examined. 



In the outer portion of the body-chamber of one specimen (PI. LXI, fig. 4) is one 

 half of the Jjjti/chus. This body is covered with oblique ribs, and lies in the longitudinal 

 line of the shell. 



The aperture is elongated (PI. LXI, fig. 6), flattened on the sides, and rounded at 

 the outer margin ; at the lower portion of the side near the spire is a projecting convex 

 lateral lappet (fig. 5), with a concavity, above which it ends in a long projecting abdo- 

 minal process, well delineated in PL LXI, figs. 5 and 6. 



Plate LXI, figs. 1 and 2, are accurate delineations of a young shell sent to me 

 for determination more than thirty years ago. The build of this shell with its fifteen 

 robust prominent oblique ribs and deep intervening valleys (fig. 2), and broad siphonal 

 area, having a central keel and lateral furrows, so closely resembled an Arietites that I 

 thought a mistake had been made when it was said to have been collected from the 

 Upper Lias of Ilminster, and I told my friend, the late Dr. Lycett, who sent the small- 

 ribbed Ammonite to me for determination, thatj if there was no mistake about its 

 horizon, it must be the young form of some larger Ammonite, which at that time we 

 did not know. It was not until many years afterwards, when I found a similar Ammonite 

 in the interior whorls of an undoubted Harp. Levisoni that the real truth dawned upon me.. 



