28 PALAEONTOLOGY 



far below the real one, since the Bryozoa of the chalk, which 

 alone have been carefully examined, amount to 213 species ; 

 while only two species are known from the trias, none at all 

 from the lias, and only five from the upper oolites, so rich in 

 corals and sponges. In the " Cours Elementaire" of d'Orbigny 

 the fossil Bryozoa are stated to amount to 1676. 



Of the 19 or 20 palaeozoic genera, none extend into the 

 secondary strata ; but of the 18 oolitic genera, Entalophora 

 and Defrancia range onwards to the tertiaries ; and Alecto, 

 Idmenea, and Eschara still survive. The oldest known fossil, 

 Oldhamia (fig. 3, 2), is supposed to be a Bryozoon. The most 

 common palaeozoic form is Fencstrdla (fig. 3, n), resembling 

 the recent " lace-coral"; there are 35 species, ranging from the 

 Lower Silurian to the Permian. One of its modifications re- 

 sembles a feather (Ptilopora, fig. 3, 10), and is found in the 

 carboniferous limestone. Another, more remarkable, has a 

 spiral axis (Arcliimcdipora, fig. 3, 9), and occurs in the same 

 formation in Kentucky. One of the oldest genera is Ptilo- 

 dictya (fig. 3, s), of which seven species are found in the Lower 

 Silurian formations. The slabs of Silurian limestone obtained 

 at Dudley are covered with myriads of small and delicate 

 fossils, including many Bryozoa. Some of these are spread 

 like a film over other fossils, and have been doubtfully re- 

 ferred to the modern genera Discopora and Bcrcnicca ; others, 

 with slender branches, and erect or creeping, are called Mille- 

 poras, Heteroporas, and Escharinas. The genus Ccenites (fig. 

 3, 7), perhaps belongs here. The magncsian limestone con- 

 tains several large " lace-corals" of the genera Fenestrella, 

 Synocladia, and Phyllophora ; and two branching species of 

 Thamniscus and Acanthocladia. The oolites afford many small 

 incvusting species related to Diastopora, and branching forms 

 like Tc rebel 'I aria and Chrysaora. In the chalk, the Escharas 

 are most numerous, and Lut/mdites and Cupularia first appear. 

 Some thin beds of the lower chalk are almost composed of 



