The Lineage of .Tragophylloceras loscombv. 223 
the degree of involution may likewise be explained by tachy- 
genesis. The following table gives details of whorl heights in 
type I, in loscombi* and in ‘ numismale.’ t 
Diameter. loscombi. Type i ‘numismale.’ 
ave. WV ent Spek Celt. nau aeer Sa aes of amet 9) 
oe Wh. th. Pein eocearea cee Bee SAGE oe CeO 
4 mms. Wh. ht. re AbOUtre:. - 40) trots 20s i AS 
‘ Wh. th. Ms Gg htes ts Bee WE: 3 pe Ae WME 1) 
7 mms. Wh. ht. ee ph tenaaae aee De ee al. | ae OA 
Hh Oy A A Ke ee 30 33 3 
It will be seen from the above that in ‘ 7. nwmismale’ whorl 
height is equal to whorl thickness at a diameter of 4 mms. ; in 
type I this condition is reached a little earlier, and in T. 
loscombi, at less than 3mms. At every stage, the specimen 
shown in fig. I is intermediate between the typical 7. loscombi 
and Pompeckj’s numismale. 
The protoconch of type 1 (fig. 1 g.h) likewise shows inter- 
esting differences from that of Tvagophylloceras loscombi. The 
former is more tumid and less distinctly fusiform, although 
the lengths of the two forms are identical, viz. about c.6 mms. 
Probably these characters also are indications of its more primi- 
tive nature. 
It will be apparent that the constricted specimens we have 
described, approach very closely in many respects to T. los- 
combi ; indeed, similarly constricted forms were described by 
d’Orbigny?{ under that name. They are still more like the fossils 
referred to numismale by Pompeckj. Buckman, § however, 
has limited the name, and separated Pompeckj’s forms and 
some of those figured by Quenstedt, as 7. typicum, which 
is a ‘crenulate, compressed development’ of numismale. 
The lineage of numismale-loscombi in all probability also includes 
Trag. ambiguus, Simps. Pompeckj stated that one of the 
differences between ‘ numismale’ (i.e. typicum, Buck.) and T. 
loscombt, lay in the smaller number of auxiliaries in the latter. 
Spath urged that this difference is no reason for doubting his 
conclusion, a suggestion which is supported by the types 
described, in which the number of auxiliaries is very variable. 
For our information concerning the constricted form, we 
have had to rely almost entirely on young material, therefore 
we cannot state its precise position in the lineage numzismale- 
ambiguus-loscombi, until the developments of the named adult 

* Spath, loc. cit. Table 1., p. 342. 
t Pompeckj, J. F., ‘ Beit. Revision. Amm. Swab. Jura,’ 1893, p. 14. 
Buckman has renamed this T. typicum. See below. 
¢ d’Orbigny, ‘ Paleont. franc. Terr. Jurass,’ Tom. 1, p. 265, 1842. 
§ Buckman, S.S., ‘Yorks. Type Amm.’, I., p. viii., 1912. 
1916 July 1. 
