8 PALEONTOLOGY. 



in the Devonian, and Bothroconis Mamillopora, and Tragos, 

 in the Permian or magnesian, limestone. Several genera are 

 common to the trias and oolites, and several more are peculiar 

 to the latter strata. The Oxfordian sponges belong chiefly to 

 the genera Eudea, Hippalimus, Cribrispongia, Stellispongia, 

 and Cupulispongia. Their fibrons skeleton appears to have 

 been entirely calcareous, and often very solid; their form is 

 cup-shaped, or mammillated, or incrusting, and many have a 

 sieve-like appearance, from the regular distribution of the 

 excurrent orifices over their surface. 



The greensand of Faringdon in Berkshire is a stratum 

 prolific in sponges, chiefly cup-shaped and calcareous, of the 

 genera Scyphia and Chenendqpora ; or mammillated, like 

 Cnemidium and Verticillopora. The Kentish rag is full of 

 sponges, which are most apparent on the water-worn sides of 

 fissures. Some beds are so full of silicious spicula as to irritate 

 the hands of the quarrymen working those beds. The green- 

 sand of Blackdown is famous for the number and perfect 

 preservation of its pear-shaped Svphonice (fig. 2, i) ; whilst 

 those of Warminster are ornamented with three or more lobes. 

 The latter locality is the richest in England for large cup- 

 shaped and branching sponges (Polypothecia), which are all 

 silicified : the long stems of these sponges have been mistaken 

 for bones. The sponges, chiefly SipJwnice, of the upper green- 

 sand of Farnham are infiltrated with phosphate of lime, and 

 have been used in agriculture. 



The sponges of the chalk belong to several distinct families. 

 Choanites resembles the Siphonia, but is sessile, and exhibits 

 in section, or in weathered specimens, a spiral tube winding- 

 round the central cavity. It is the commonest sponge in the 

 Brighton brooch-pebbles. Others are irregularly cup-shaped 

 and calcareous ; and many of the Wiltshire flints have a 

 nucleus of branching sponge (S. clavellata). The chalk flints, 

 arranged in regular layers, or built up in columns of " Para- 





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