274 
INFERIOR OOLITE AMMONITES. 
Writing- to me in May, 1889, Dr. Hang says that my " Hollandfe " that is the 
specimen depicted in PI. XLVIII, figs. 4, 5, is Dumortier's " Begleyi," and that 
he would separate " Bsgleiji " from " scissus." I am under great obligations 
to my friend for the interesting and critical remarks which his letters contain, 
and, even if I am not able to agree with them, they are none the less valuable as 
an assistance in forming a judgment upon any given question. In the present 
case it is merely a matter of convenience. If the specimen shown in figs. 4, 5, be 
called Begleyi," the more evolute form (figs. 1 — 3) must pass as " scissus," and 
the close-ribbed form (figs. 8 — 10) mnst be a new species. There certainly are 
difierences between the three specimens ; and whether one treats them as species 
or as varieties — incipient species — is not of much moment so long as we 
recognise the true biological position of the different forms. I prefer for the 
present to use the name " scissus " comprehensively. 
The three specimens figured show a gradual change in the normal manner 
- — for instance, the whorls are more quickly coiled, more compressed, and broader, 
while the ribs are more approximate and less conspicuous in figs. 1, 2, 4 — 5, 
8 — 9. In the ventral area, too, they exhibit, roughly speaking, a gradual change 
towards deeper sulcation ; but each has also certain different features. The ventral 
area of figs. 1, 2, is not sulcate in the interspaces ; while the ribs which rise up 
in an obscure tubercle suddenly decline with a slight forward twist, and are 
obscurely joined by a V-shaped loop (fig. 3). In figs. 4, 5 the ventral area is 
sulcate all around ; the ribs commence the forward bend on what may be called 
the edge of the ventral area, and have a well-marked forward twist (fig. 6). In 
figs. 8, 9 the ventral area is somewhat ill-preserved, but it is furrowed ; the 
ribs come right up to the parting without any twist, they are straighter than 
those of the first specimen, and they rise into a small tubercle, and then decline 
with a small twist. 
Yv^e^s^?-^ OettvM&ceras scissum is a rare species in this country. It is always of very 
small size, not exceeding two inches in diameter ; while for Continental examples 
Vacek figures one 3f inches, and Benecke's fossil was 2f inches across. 
I think it would be safe to say that this species occurs in the Opaliniim- and 
Miorcloisouge-zones, and that generally the specimens of the 3Iurchison^-zoue^ are 
more involute with closer, finer ribs than those in the lower zone — they are, m 
fact, degenerate. Burton Bradstock, Dorset, is the principal locality, the species 
occurring with Lioc. opalinum at the top of the zone.^ Other localities have 
1 The Murchisonce- aud Opaliniim-zones. are very intimately connected at many places in tb.? 
south country. Sometimes they have practically coalesced, as at Symonsbury Hill, near Bridport. 
(See "Down Cliffs," ' Quart. Journ. GleoL Soc.,' vol. xlvi, p. 520, 1890). 
2 Tor detailed sections of Burton Bradstock, see Hudleston, " Gasteropoda," 'Pal. Soc.,' p. 31. 
vol xl, 1887 ; and also my paper, " Cotteswold, Midford, and Teovil Sands," ' Quart. Journ. Geol. 
Soc.,' vol. xlv, p. 451, 1889. 
