MULTILOCULAR SHELLS. 247 



size, occurs in the grey limestone at Malton. — The a. angulatus of 

 Sowerby, Tab. 107, Fig'. 1, which occurs in nodules in the alum shale, 

 is on the contrary a much thicker shell than a. communis, though the 

 ribs have nearly the same form. 



No. 8 also resembles No. 3, both in size and in form ; but differs 

 from it in being rather more flat, and especially in the slenderness of 

 its ribs, from which we may name it a. tenuicostatus. Like a. angula- 

 tus, it is not very plentiful. 



No. 1 is very abundant in the alum shale, and often attains a 

 great size, measuring six or eight inches, or upwards, in diameter. It 

 is the a. Walcotii of Sowerby, Tab. 106. We would rather name it 

 a. Hildensis, in honour of our Lady Hilda. It is more flat than a. 

 eommicnis, and has fewer whirls. The back has a keel between two 

 fuiTows. The ribs are somewhat sigmoidal, especially near the 

 mouth, where the shell when entire also displays minute sigmoidal 

 stria;. A furrow, more or less deep, usually divides each whirl into 

 two parts, and on the inner part the ribs are rather faintly marked. 

 In this respect, however, there is much variety in the shells of this 

 species. Most specimens are only casts, and display the elegantly 

 ramified edges of the septa, resembling flowers. The original shell 

 appears from its remains in some specimens, to have been of a choco- 

 late brown colour, handsomely spotted with white. 



No. 2 is a very reduced figure of what we may call a. ingens, 

 being one of our largest ammonites. The specimen is from the oolite 

 at Pickering, and measures fourteen inches broad, and four in thick- 

 ness at the aperture, which is nearly round, with a slight approach 

 to quadrangular. It weighs twenty-nine pounds. The ribs are strong, 

 but not very numerous, and are discontinued on the back : in which 

 respect it differs from a. giganleus (Sowerby, Tab. 126), a large shell 

 which also occurs in the Pickering and Malton oolite; the ribs of 

 which are very numerous, and each of them on tlie back is parted 



