100 INFERIOR OOLITE AMMONITES. 



frequently crushed out of shape ; and, as this rarely, if ever, occurs with any other 

 species in this zone at Bradford Abbas, it may be considered as due to natural 

 weakness in the structure of the shell itself. Its peculiar shape and rather simple 

 sutures suggest such an idea. The form /3 is far scarcer than the other. 

 Incomplete specimens of six inches in diameter occur. Both forms, « and /3, have 

 been found by Mr. E. Witchell in the Gryphite-grit of Frith Quarry, near Pains- 

 wick, and of Rodborough Hill, near Stroud (see p. 91). 



Plate XIX, fig. 3, represents a side view of the form a with a large proportion 

 of the test well preserved ; fig. 4 is an exact outline of the front view. The side 

 view of the form /3 is shown in fig. 1, but only a small amount of test is preserved ; 

 fig. 2 exhibits the front view, and the sloping subconcave inner margin can be 

 seen. Both these specimens came from Bradford Abbas, Dorset. Plate A, 

 fig. 25, exhibits the suture-line of this species, taken from the last-mentioned 

 specimen. 



Htpeelioceras subdiscoideum, S. Buckman. Plate XIX, figs. 5 and 6 ; Plate XX, 



figs. 1 and 2 ; Plate A, fig. 26. 



It is not intended to definitely separate the specimens of which these figures 

 exhibit two typical individuals, until more material shows that their peculiar 

 characteristics are fairly constant. The name must therefore be considered as 

 provisional only. Whatever value may be attached to a name, it is useful, if only 

 for purposes of registration ; and it can scarcely be denied that these specimens 

 could not be included in any other of the species of Hyperlioceras without some 

 distinctive appellation. To me they do not appear a variety of any of the foregoing 

 species, but more probably a fixed mutation of some species belonging to the 

 Murchisonee-zone, and are therefore cousins to those previously described. This 

 species (as I will call it for the present) appears to unite Hyperlioceras discites and 

 H. discoideum ; or rather (to speak with exactness) it appears to unite Hyperlioc' 

 discites I and H. discoideum /3. From the former it differs by showing no trace of 

 the concavity in the inner lateral area, and by the outer portion of the aperture 

 being somewhat more attenuated ; from the latter, by possessing a more quadrate 

 aperture and a larger umbilicus ; while it differs from both in possessing slight 

 ribs at a later period, and a somewhat differently constructed umbilicus. This 

 feature I will explain as follows : The appearance of the inner whorls indicates a 

 more open, depressed specimen in youth, ornamented with ribs ; but a change 

 takes place, and the umbilicus becomes proportionately rather narrower and 

 deeper, with upright, sometimes almost overhanging, inner margin. Yet another 



