342 CRETACEOUS GASTROPODA 
3. Nerira rugosissima, Forbes, sp. Pl. XXV, Fig. 6. 
1846. Natica rugosissima, Forbes, Trans. Geol. Soc., Lond., VIL., p. 137, Pl. XIV, Fig. 7. 
idem, @’Orbigny, Pictet, Gabb, and others. 
Ner. testa sub-rotundata, sub-globosa ; anfractibus tribus, postice prope suturam 
canaliculatim depressis composita, spira vie elevata; ultimo anfractu convexo, 
transversaliter costulis numerosis crispatis, sub-acutis ornata, costulis im parte 
anteriori sulcis angustis, decussantibus interruptis ; apertura dilatata, labio angusto, 
declivi, postice incrassato, antice imsinuato, intus i margine multi-dentato. 
A small sub-globose shell, consisting of three volutions, which are posteriorly 
somewhat depressed. The spire is very slightly prominent; the last whorl convex, 
ornamented with numerous sharp, undulating ribs, which are on the anterior 
portion interrupted by narrow sulcations. The form of the inner lip is very 
peculiar; it is narrow, precipitous, posteriorly much thickened and anteriorly widely 
insinuated; the inner edge is provided with six rather fine teeth on the insinuated 
portion, the posterior one not being clearly traceable. 
This peculiar species was first described by Prof. Forbes as a Natica, but the 
form of the inner lip places its present generic determination beyond any doubt: 
the sharp undulating ribs distinguish the species from any other known Nerita. 
Locality—The only figured specimen was found in a light coloured calcareous 
sandstone 8. E. of Parchairy ; Prof. Forbes quotes it from Verdachellum. 
Formation.—Arrialoor group. 
_ Il. Tribe, Ciliipedata.* 
We place in this tribe all the different genera of shells, which are usually 
described in the family Trocurpm or Trocuacea. The animals are true Proso- 
BRANCHIA SCUTIBRANCHIATA, that is, they have only one branchial plume, consisting 
of two series of lamelle, which are placed on either side of a thin membrane. 
The principal characteristic of the animals lies in the presence of a lateral fringe, 
which generally originates at the external side of the eye-pedicles, and continues 
laterally for some distance on the upper part of the foot, on either side. The 
filaments on the fringe are sometimes short, numerous, and all of equal size, as for 
instance, in the Svomarirp#, but generally there are three or four pairs of them 
much longer, as in most of the species belonging to the other families. The tentacles 
are usually thin and long. The head is provided with a short and thick rostrum, 
which is sometimes retractile. The teeth of the radula are distinguished by a large 
number of equally formed laterals, an arrangement common to many families which 
are classed by Troschel, Lovén, partially by Gray and others, in the sub-order 
RuIPrmDocLossa. Comparing the general structure of the teeth of the CrnirpEpaTa 
with those of the PLANILABIATA it may be observed, that the former have the 
central teeth generally sub-equal and the laterals tolerably thick, while the latter 
have the central teeth rather unequal and the laterals very thin. 
* With reference to the presence of a ciliated fringe on the foot. 
