DORSETENSIA EDOUARDIANA. 
305 
rather acutely carinate and sloping in the involute examples. Inner margin 
undefined in the evolute forms, upright and sharply defined in the involute 
specimens. Inclusion one-third to one-half. Umbilicus slowly coiled, scored with 
numerous straight ribs. Suture-line simple ; the superior lateral lobe broad, but 
not longer than the siphonal ; the inferior lateral lobe and the auxiliaries rather 
elevated. 
I have applied the specific name " Edouardiana " to a series of examples which 
show the phases of a gradual change from evolute, sulcate-carinate, strong-ribbed 
whorls to somewhat involute, carinate, obscurely-ribbed whorls. Five varieties 
illustrating four steps in direct developmental variation are depicted in PI. LII, 
namely : — 
a. Evolute, coarse distant ribs, carinate-sulcate ventral area (figs. 8, 9). 
aa. Evolute, finer closer ribs, ventral sulci shallow — in fact, the carina is 
bordered by a smooth flattish area (figs. 11, 12). This form is a side shoot of a. 
j3. Compared with a, less evolute, ribs closer (figs. 15, 16). 
•y. More involute, ribs becoming inconspicuous on end of whorl, ventral sulci 
obsolete, inner margin defined on last half of last whorl (figs. 18, 19). This is the 
form which agrees exactly with d'Orbigny's figure. 
S. Still more involute, ribs obsolescent, ventral area subacutely sloped ; inner 
margin conspicuous (figs. 21, 22). 
The variety y appears to lead directly into Dorsetensia jpulclira, and so to 
" Romani," Oppel ; while the variety S apparently leads into Dorsetensia com- 
planata, with a link missing (page 307). In general appearance, and in the style 
of its ribbing, Dors. Edouardiana recalls the species of Grammoceras and 
Dumortieria. Its suture-line, however, prevents confusion with the latter ; while 
the inner coronetted whorls (PI. XLIX, fig. 4 ; PI. LII, fig. 14) indicate its 
separation from Grammoceras, and are a feature of generic value. It may be 
urged that this feature is not always observable ; but Grammoc. toarcense is the only 
species which Dors. Edouardiana is like ; and that species is not nearly so slowly 
coiled, and has innermost whorls conspicuously smooth.-^ 
The suture-line of my specimens has a considerable likeness to that of 
Grammoceras. D'Orbigny, however, drew the suture with a very long superior 
lateral lobe ; but I do not find this character in any species of the genus. 
This is decidedly a scarce species ; and it was not till after I had written my 
paper on Inferior Oolite Ammonites (see synonyms) that any of the involute 
varieties were found. The Him-phriesianum-zone is the horizon of this species ; 
while Sherborne and Oborne in Dorset, and Milborne Wick, Somerset, are the 
only locaUties. My father was in error in attributing this species to Bradford 
Abbas — his specimens are now before me, and their matrix shows conclusively 
^ See page 171. 
39 
