The Warminster Greensand Fossils. 271 



When we come to study the components of this fauna we find it 

 to be a curious mixture of species, many of them being species which 

 are common in the Chalk Marl, and are not known to occur below 

 this particular bed of sand or its equivalent on the south coast, 

 while others are species which do not range higher, or are, at any 

 rate, not found in the Chalk Marl. Considering the stratigraphical 

 position of the Rye Hill Sand and the upward passage from it to the 

 Chloritic Marl, it is not surprising to find that the fauna also exhibits 

 a transitional character. It will, however, be useful to discuss the 

 evidence afforded by the members of each class or order separately. 



Cephalopoda. — All the Ammonites and most of the other Cepha- 

 lopods are species which characterize the true Chloritic Marl (zone 

 of Stanronema Carteri) and the Chalk Marl (zone of Ammonites 

 varians). So far as my experience goes, none of them, except 

 Belemnitella ultima, Nautilus subradiatus, and Ammonites planidatus, 

 range down to lower horizons. 



Gasteropoda. — It is doubtful how many of these really occur in the 

 Rye Hill Sand ; they are certainly rare, and most of those in museum 

 collections have come from the Chloritic Marl. Of those admitted 

 to my list, the range of most is probably upward as well as downward. 



Lamellibranchiata. — The distribution of these is remarkable; only 

 four of them range down, no less than 10 have an exclusively 

 upward range, while 12 range both up and down, and six are 

 doubtfully identified with French Cenomanien species. This part 

 of the fauna, then, has decidedly closer relations with that of the 

 Chalk Marl than with that of the Greensand. 



Brachiopoda. — Of these, again, only four are exclusively Green- 

 sand species ; and one of these, the supposed Rhynchonella sulcata, 

 is probably an extreme variety of Rh. dimidiata. Seven species 

 belong decidedly to the Lower Chalk fauna, and eight are believed 

 to range both up and down. 



Crustacea. — Of these, five range down to the Gault, two are 

 peculiar to the Rye Hill Sand, and only Scalpellum lineatum ranges 

 into the Chalk. The Brachyurous Crustacea seem, therefore, to be 

 the relics of an older fauna, and as none have yet been found in the 

 Chalk Marl it would seem as if the physical conditions of that 

 deposit were unsuitable to them. 



Annelids. — These are long-lived creatures, but most of the species 

 in the list range upward ; and though some range down as well, only 

 one is specially a Greensand species. 



Echinodermata. — Out of a total of 28 species nine are rare fossils, 

 either unknown elsewhere in England at present, or found only in 

 the Cenomanian of Devon. Deducting these nine, the remainder 

 is 19; and of these, 11 range upward, occurring either in Chloritic 

 Marl or Chalk Marl, five range both up and down, while only three 

 are not known to occur at higher horizons. One of the last, 

 Cardiaster fossarius, is very characteristic of the higher part of 

 the Upper Greensand in the south and south-west of England. 

 It is common in the Chert Beds near Warminster, but seems rather 

 rare in the Rye Hill Sand. 



