118 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



perfect manner, including the thin tests of Pholadomya, Myacites, Gresslya, Goniomya, and Cercomya, 

 together with the outer, granulated tegument of the four latter genera ; and when the matrix is less hard, 

 even their internal hinge characters may be disclosed. The Gasteropoda are few, both as to species and 

 individuals ; the Cephalopoda are, with the exception of a small Belemnite, limited to Ammonites macro- 

 cephalus, which affords great variety in the details of its figure and ornamentation, but which never attains 

 to the large dimensions of Wiltshire specimens. 



Its Molluscs, viewed comprehensively, may be regarded as n transitive series, a chain of life serving to 

 connect the fauna of the Inferior Oolite with that of the Oxfordian rocks, comprising a considerable 

 proportion of the former, perhaps an equal number of special forms, a much smaller number of species 

 which pass upwards into the Oxfordian beds, and a still lessening proportion of forms which are recognised 

 in the Great Oolite or Forest Marble, but these latter consist almost entirely of shells which pass upwards 

 from the Inferior Oolite. 



Minute Testacea of the Great Oolite and Forest Marble. 



Only a portion of these have been selected for illustration, others, inconveniently minute, having been 

 rejected upon that account. That some of these minute forms attain to much larger dimensions under 

 different conditions may be inferred from the fact that many minute Gasteropoda and Conchifera associated 

 with them are only dwarfed forms of well-known Great Oolite species, which in other beds are of the 

 dimensions figured in the former parts of this Monograph. 



Forest Marble Testacea. 



The following note, kindly communicated by Mr. Walton, describes the localities of the Forest Marble 

 cited in this Monograph : 



" The principal localities from which these fossils have been obtained are Farleigh, Hungerford, in 

 Somersetshire ; Pound Pill, near Corsham, and Laycock, in Wiltshire ; and Burton Bradstock, about five 

 miles from Bridport. The lithological character of the Forest Marble is very various, demonstrating the 

 littoral character of the deposit, which is shown also by the trails of animals and the numerous remains of 

 what can hardly be anything but Fucoids. The best locality at Farleigh is a superficial cutting opposite 

 Wick Farmhouse, made in forming the new Warminster Road, and the bed is a crumbly, shelly marl, and 

 the fossils, when first found, apparently mere lumps of clay. In the small quarries near Hinton Charter- 

 house, Cumberwell, and Philips Norton, the rock is a hard, calcareo-arenaceous stone, and at Pound Pill 

 it is as hard and more intractable than Carboniferous limestone. At the railroad-cutting near Laycock it 

 is a cream-coloured clay, containing shells better preserved than usual, and from this nearly all the small 

 shells have been procured. In many places the Forest Marble is a mere mass of broken shells, and 

 frequently formed almost exclusively of crushed Rhynchonellae. At Burton Bradstock the Forest 

 Marble clay rests on the lower beds of the Inferior Oolite, and most of the fossils from that locality were 

 picked up from a bank on the sea-shore. I have never found an Ammonite in the Forest Marble, and only 

 one very doubtful trace in the Cornbrash." 



Testacea from the Clays of the Forest Marble compared with those from the Limestones of the Great 

 Oolite. As might be anticipated from the widely differing mineral conditions of the two deposits, they are 

 tenanted to a great extent by different races of Molluscs. The fossils figured in this Supplement from the 

 Forest Marble by no means represent the whole of the additional species contained in the clay beds of that 

 stage, but such only as from their state of preservation are suitable for our plates ; a large proportion have 



