228 The Chalk 



Judd, also occur in the Island of Mull beneath the 

 Miocene basalts. 



About half the genera, and a considerable number of 

 Chalk species, are identical with those of the Grault and 

 Upper Grreensand, but it contains a far greater number, 

 nearly 800, most of which are peculiar to itself. 

 Plants are few, as might be expected in a wide deep-sea 

 deposit. A great many Sponges have been described, 

 chiefly from flints. Among the most numerous are 

 species belonging to the genera Ventriculites, Cephalites, 

 Spongia, and Siphonia. A large number of genera 

 and species of Foraminifera are also described, among 

 which Globigerina bulloides, Dentcdina gracilis, and 

 Rotalina ornata, are common. Of Corals about 15 

 species are known, several of which belong to the genus 

 Parasmilia (centralis, &c.), CaryophUlia Icevigata, 

 &c. Echinodermata are very numerous, among others 

 including the genera Ananchytes, Cardiaster, Cidaris, 

 Cyphosoma, Diadema, Echinopsis, Galerites and 

 Echinobrissus, Holaster, Micraster, and Solenia, &c. 

 Among its starfish are comprised the genera Arthraster, 

 Goniaster, and Oreaster. Of these Groniaster is exceed- 

 ingly characteristic. In addition it has yielded an 

 Ophiura, and several Crinoids, Bourgueticrinus el- 

 lipticus, Marsupites Milleri, &c. On shells, &c., found 

 in the Chalk, are frequent Serpulse. It also yields 

 Cirripeds and a few Crustaceans, Enoplodytia Sussex- 

 ensis, &c. Polyzoa are numerous, of many species. 

 Like other members of the Cretaceous rocks, its Brachio- 

 poda generically resemble those of the Oolites, including 

 Rhynconella, Terebratulina, and Terebratula. The 

 Lamelli branchiate molluscs of the Chalk are in some 

 cases specifically identical with those of the Grault and 

 Upper Grreensand; and, generically, they bear the 



