232 CRETACEOUS GASTROPODA 
2. ScALA SUBTURBINATA, D’Orbigny, Pl. XVIII, Figs. 2-8. 
1846. Scalaria turbinata, Forbes, Trans. Geol. Soc., Lond., VI, p. 124, Pl. XII, Fig. 18 (non idem Conrad). 
1850. x subturbinata, D’Orb., Prod. II, p. 217. 
1861. & Haidingeri, Binkhorst, Mon. Gast. et Ceph. Limbourg, p. 36, Pl. II, Fig. 4. 
Sc. testa turbinate-conica ; anfractibus valde convexis, transversaliter costatis, 
spiraliter minute striatis, costis 14-15 in un circuitu, crassis, prope rectis, carinam 
ad peripheriam basis ultimi anfractus sitam transeuntibus ; striis alternatim forti- 
oribus et tenuioribus ; apertura ovate rotundata, antice paulo producta, sub-effusa ; 
marginibus parum expansis. 3 
Spiral angle 35°; sutural angle 10°. 
Height of last whorl : total of shell ... — .. (considered as 1:00) ew 0°35. 
Height of penultimate whorl : height of spire (__,, PMS) vee 0°29; 
” ” ” ” : its width eos. ( ” mp ep) we 0°48. 
The characteristics of this species consist in the short conical form, great con- 
vexity of the whorls, strong transversal ribs and alternately stronger, but compar- 
atively fine, spiral striee. The ribs cross on the basis of the last whorl a thin keel, 
which is placed near to, but not quite on the edge of, the periphery, and continue 
towards the centre, decreasing gradually in thickness. The edge of the transverse 
ribs is originally sharp, but when, with advancing growth, it wears off gradually, 
the ribs appear rounded, as usual in species of Scala; sometimes this edge is, 
however, broken off, and in such cases a furrow appears in the middle, indicating 
the separation of the two lamelle, which compose each of the ribs. All these 
characters agree so exactly with Binkhorst’s figures and descriptions, that it 
is impossible to point out a difference between the two fossils. An examination 
of Binkhorst’s originals has confirmed this statement. Forbes’ figure is not charac- 
teristically drawn, and might be applied rather to the next species, but the original 
specimen in the London Geol. Soc. Collection belongs certainly to this. It is 
instantly recognised by the coarser spiral striation. In our small specimen, re- _ 
presented in Fig. 2 on Pl. XVIII, the aperture is perfect, being roundish-oval, 
anteriorly somewhat produced, sub-effuse, with slightly enlarged margins. 
The beds from which the species has been described by Binkhorst belong to 
the characteristic Maestricht Chalk. Prof. Forbes’ original specimen appears to be 
from the Verdachellum sandstones. 
Locality. —S. W. of Arrialoor, in whitish siliceous sandstone ; rare. 
Formation.—Arrialoor group. 
