POLYMORPHIDtE. 
281 
in a different degree. Thus the sulcate-carinate ventral area, wliicli is so 
conspicuous among tlie Arietidse, exists among the PolymorpMdse practically only 
in Gatulloceras aratum, and one or two other allied species ; though Gatullocems 
Dumortieri shows what may be regarded as nascent furrows (PL XXXIX, fig. 8). 
I described this species in the explanation of PI. XXXIX as a Bumortieria, 
thinking it might have been an aberrant mutation of Bum. Levesquei which had 
acquired ventral furrows ; but further consideration leads me to regard it as more 
probably a more quickly-coiled, compressed mutation of Gatull. Ferroiidi ; and the 
furrows of the latter species undoubtedly support this view. 
My species has a general resemblance to Gatulloceras Meneghinii (Zittel) ;^ but, 
as Dr. Haug points out to me, its whorls increase more rapidly. Its ribs are also 
more reclined laterally and more inclined ventrally ; it is thicker and squarer ; while 
its ventral furrows are pronounced. It is interesting to notice that there is just a 
suspicion of ventral furrows indicated in Meneghini's figures of Gatull. Meneg- 
hinii. Prom Gatull. Perroudi my species differs in being more quickly- coiled and 
more compressed. 
Neither the locality nor the horizon of the larger specimen has been recorded. 
Judging from the matrix, however, I have little hesitation in stating that it came 
from Trent, Somerset, from the so-called " Upper Lias," that is to say, from just 
below the Yeovil Sands. Possibly the uppermost part of these beds is equivalent 
to beds 3 or 4 of the White-Lackington section (p. 165) ; and, if so, the specimen 
came from the lower part of the Jurense-zone. The smaller specimen came from 
the Bumortieria-heds {Jurense-zone) of Penn Wood, near Stroud, Gloucestershire. 
The larger specimen is figured in PI. XXXIX, figs. 1, 2, 2a. It possesses the 
test, but in a rather inferior condition in places. The ventral furrows are marked 
on the test as clearly as on the core. The smaller specimen is figured in 
PI. XXXIX, figs. 3 — 5 ; it lacks the test entirely. These are the only two speci- 
mens I have seen — the former was in my father's collection ; and the latter I 
collected myself. 
Resume op the " Polymoephid^." 
The species of the Folymorphidse which have come within the scope of this 
Monograph are interesting, because they exhibit both primitive and highly- 
specialised forms ; and also because they illustrate the various developments which 
have arisen from one radical stock by different modifications. In fact, the four 
^ Am. Levesquei, Meneghini (non d'Orbigny), 'Pal. Lombarde, Serie iv, pi. x, figs. 4, 5. 
36 
