L. F. Spath — On Schlotheimia Greenoughi. 99 



(B.M. No. 82363) has a diameter of 520 mm. Wright does not 

 mention that he had two specimens ; but his figure evidently is 

 a composite one, the obscure costse of the outer whorl showing on 

 the former specimen only, though in a less distinct manner. Moreover, 

 whereas his figured specimen has the locality "Somerset" attached 

 to it, Wright says that no locality was recorded, which again is the 

 case with C, Sowerby's specimen of 440 mm. diameter. Wright 

 thought that it probably came from Lyme Regis, "from the peno- 

 logical character of the matrix in which it was embedded," but this 

 is doubtful, as also is Morris's 1 mention of the species from Lyme 

 thirty-nine years earlier, and the record of A. Greenoughi from the 

 \_oxynotum zone ? of the] neighbourhood of Cheltenham both by 

 J. Buckman 2 and by S. S. Buckman. 3 



Sowerby's specimen C of 440 mm. diameter has the following 

 dimensions : — 



Height, 42 per cent of the diameter. 



Thickness, ? 24 



Umbilicus, 29 ,, ,, 



On comparing these dimensions with those of the lectotype (B) it 

 will be seen that, whereas the height of the whorl has diminished 

 from 47 to 42 per cent, the umbilicus has widened considerably 

 (from 21 to 29 per cent). It appears probable that this is the 

 normal development of the form, i.e. that it is a case of latumbilication 

 arising from excentric coiling. And specimen C, indeed, clearly 

 exhibits this excentrumbilication, though not the specimen figured 

 by Wright. The latter has at a diameter of 520 mm. the following 

 dimensions : — 



Height, 42 per cent of the diameter, 

 Thickness, ? 24 ,, 

 Umbilicus, 30 ,, ,, 



whereas his (reduced) figure shows — 



Height, 41 per cent of the diameter, 



Umbilicus, 31 ,, ,, (34 per cent in the text). 



These dimensions agree well with those of the large specimen (C) 

 mentioned above, and also show that Wright's delineation was fairly 

 accurate so far as the dimensions are concerned, although in the 

 absence of a sectional view the shading suggests thicker whorls 

 and the obscure costae on the body-chamber are too pronounced. 

 Important differences appear, however, when we compare the 

 costation of the inner whorls of these two large specimens with 

 that of the lectotype. The latter has, counting backwards from 

 the last rib at a diameter of about 145 mm., twenty and fifteen 

 primary costae respectively for these two whorls. They give rise 

 to about two or three secondaries each, and these are continuous 

 across the periphery at a diameter of 90 mm. when they weaken 

 and finally, at 200 mm. diameter, almost entirely disappear. 



1 John Morris, Catalogue of British Fossils, 1843, p. 173. 



2 In Murchison, Geology of Cheltenham, 2nd issue, 1845, p. 89. 



:i In Eichardson, Geology of Cheltenham, 1904, p. 212 (as Agassiceras 

 \_Agassizoceras~] Greenoughi) . 



