lii PEOCEEDINQS OF THE GEOLOGICAL SOCIETY. 



Witli the Foraminifera, however, end the specific identities be- 

 tween the Chalk and the Atlantic mud. Beyond this group we find 

 resemblances or afiinities only. Siliceous sponges, of which no less 

 than 20 genera have been dredged, abound, it is true, as they do in 

 the Chalk ; but they are either new forms, or are Mediterranean 

 and Azorean species. Professor Thomson * remarks that the Ven- 

 triculites of the Chalk are represented by the group of Porifera Vitrea, 

 that the species of Sijmpagella, Holtenia (Sphceroma), and Farrea 

 approach the Siphonias and Ventriculites very nearly, but that they 

 form a distinct subsection of the order. Echinoderms abound, as in 

 the Chalk ; and species of the genus Cidaris are numerous, while 

 some forms of Diademidce approach the curious Echinotliuria of the 

 Chalk. The " Salenite, CassidulidiB, and Dysasters approach their Cre- 

 taceous antetypes more closely than any known forms ; but they are ' 

 generally dwarfed, and otherwise diverge so far as to require in most 

 cases the establishment of new genera for their accommodation." ■■ 

 The Bourgueticrinus of the Chalk is represented by the beautiful 

 BMzocrinus, first found by Sars ofi' the coast of N^orway, and after- 

 wards by the ' Porcupine ' expedition in the North Atlantic ; and the • 

 Brachiopoda are represented by the smooth forms of Terehratula so ' 

 common in the Chalk ; while the T. ( Waldheimia) cranium may be 

 considered a Chalk type. 



Dr. Carpenter further remarks upon the occurrence of numerous 

 arenaceous forms of Foraminifera analogous to the gigantic forms 

 discovered in the Upper Greensand by Prof. Morris ; and there is 

 one that can certainly be identified with a form lately discovered 

 by Mr. Brady in a clay-bed of the Carboniferous Limestone f. The 

 presence of the Xanthidia, so frequently preserved in chalk flints, 

 is also observed in the Atlantic mud. Some southern forms of star- 

 fishes are found dwarfed from a diameter of 6 inches to one of 

 2 inches, together with a number of Echinoderms previously known 

 only as Norwegian or Arctic. On the other hand the Foraminifera 

 are large, as in warm climates or in Tertiary beds, or as with the Cris- 

 tellarian and Milioline groups. Amongst fishes a Beryx was found, 

 a genus of which there are 4 species in the English Chalk. 



It is also to be noticed that we have in the Chalk the first repre- 

 sentatives of the cycloid fishes, which have their maximum develop- 

 ment in existing seas, and that, of the 103 genera of testaceous 



* 'Nature 'for July 1870. 



t It was in beds of this age that Prof. Phillips, some time since, indicated the 

 presence of Globigerina. 



