MIDDLE CHALK—GENERAL ACCOUNT. 
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Owen as obtained from the chalk-pit at Houghton, near Arundel, 
and the larger pits there are in Middle Chalk. 
Mr. Hill found a tooth of Polyptychodon in the zone of Holaster 
planus at Dover. 
Pisces.— Remains of Fish are abundant in some localities, 
especially in the counties of Kent and Sussex. Many of the species 
are the same as those occurring in the Lower Chalk, such as 
Ptychodus decurrens } Pt. mammillaris, Macropoma Mantelli and 
Beryx (Ctenothrissa) radians. There are also a few such as Oxyrhina 
crassidens and Ptychodus Oweni, which have as yet only been 
recorded from Middle and Upper Chalk. 
Cephalopoda.— Kemains of large Ammonites occur occasionally 
in the lower part of the Middle Chalk, and the small species Am. 
[ Prionocyclus ] Neptuni has been found by myself in Devon and 
identified by Mr. H. Woods. The following is a complete list of 
the species which have been recognised in this stage: — 
Ammonites [Haploceras] catinus, Mant. 
„ [Acanthoceras] Cunningtoni, Sharpe 
„ [Haploceras] lewesiensis ? Mant. 
„ [Prionocyclus] Neptuni, Geinitz 
„ [Acanthoceras] nodosoides, Schlilter. (Fig. 56.) 
„ [Pachydiscus] peramplus, Mant. 
„ [Acanthoceras] rusticus, Sow. 
„ [Prionotropis] Woolgari, Mant. 
Gasteropoda. —Fossils of this class are very rare in the Middle 
Chalk, except for occasional specimens of Pleurotomaria perspec- 
tiva, but Aporrhais Mantelli, and Solariella gemmata ( =Turbo 
gemmatus ) have also been found. 
Lamellibranchiata. —The commonest bivalves in the Middle Chalk 
are species of Inoceramus (Figs. 57 and 58); the lower beds are 
the home of Inoc. mytiloides (the I. labiatus of French geologists), 
and the higher beds contain Inoc. Cuvieri with other species not 
yet clearly defined. Spondylus spinosus (Fig. 61) first occurs in the 
Terebratulina zone, and thence ranges upwards into Upper 
Chalk. A few others, such as Pecten Beaveri, Ostrea vesicular is, 
and Spondylus latus, range up from the Lower Chalk. 
Brachiopoda.— In the Middle Chalk Brachiopods are often very 
numerous individually, but do not belong to many different species, 
and the following are those usually found, all except Terebratulina 
lata, ranging up from below. : — 
Bhynchonella Cuvieri, d'Orb. (Fig. 62.) 
Terebratula semiglobosa, Sow. (Fig. 60.) 
Terebratulina gracilis, Schloth, var. lata. Eth. (Fig. 59) 
„ striata, Wahl. 
Echinodermxta. —Members of this class are fairly abundant 
throughout the Middle Chalk, but more especially in the lower 
portion, and, so far as I know, only three species range up from the 
Lower Chalk; these are Galerites castanea, Hemiaster minimus 
