With the Foraminifera, however, end the specific identities be- tween the Chalk and the Atlantic mud. Beyond this group we find resemblances or affinities 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 Ventriculites of the Chalk are represented by the group of Porifera Vitrea, that the species of Sympagella, Holtenia (Sphoeroma), 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 Diademidoe approach the curious Echinotheria of the Chalk. The " Saleniae, Cassidulidae, and Dysasters approach their Cretaceous 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 Rhizocrinus, first found by Sars off' the coast of Norway, and afterwards by the ' Porcupine ' expedition in the North Atlantic ; and the Brachiopoda are represented by the smooth forms of Terebratula 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 †. The presence of the Xanthidia, so frequently preserved in chalk flints, is also observed in the Atlantic mud. Some southern forms of starfishes 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 Cristellarian 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 representatives of the cycloid fishes, which have their maximum development in existing seas, and that, of the 103 genera of testaceous
- 'Nature' for July 1870.
† It was in beds of this age that Prof. Phillips, some time since, indicated the presence of Globigerina.
