354 MESSES. H. A. OTCEOLSON AND E. ETHEKIDGE 



the Upper Silurian rocks of England, Sweden, and the United 

 States ; and we have found our progress greatly impeded by the 

 Yery unsatisfactory condition in which Alveolites stands at pre- 

 sent. Not only does it appear to be evident that the n&me Alveo- 

 lites covers a number of forms which are not always united by 

 relations of genuine affinity, but even those forms which may 

 be regarded as the types of Alveolites are only separable from cer- 

 , ._ ^xxxca gioups by characters aniio„H; to define or discover, and 

 sometimes of dubious value and uncertain in Lcx-^rp.tation. Under 

 these circumstances, it may not be useless that we shouIJ lay 

 before our fellow workers the results of our researches so far as 

 they have gone at present, more by way of discussion and sug- 

 gestion than of dogmatizing or of laying down positive conclusions 

 or formulating final definitions. 



The genus Alveolites was originally founded by Lamarck in the 

 first edition of the ' Systeme des Animaux sans Vertebres ' (pub- 

 lished in 1801), p. 375, for the reception of a single Devonian spe- 

 /cies which he described under the names of A. suiorbictdaris and 

 A. escharoides, and for which the former title has been subse- 

 quently retained. The original definition is, " Poiypary stony, 

 thick, globular or hemispherical, formed of numerous concen- 

 tric layers, which are superimposed one upon the other, each 

 layer formed by the union of alveolar, subtubular, prismatic, con- 

 tiguous cellules [or tubes], forming a network on the surface." 

 In the ' Hist. Nat. des Anim. sans Verteb.' (published in 1816), 

 vol. ii. p. 184, the same definition is given with very slight alte- 

 rations, the principal change being that the genus is now made 

 to include incrusting forms. In the second edition of Lamarck's 

 'Hist. Nat. des Anim. sans Vertebr.' (published in 1836), the 

 portion relating to the corals was revised by Milne-Edwards, and 

 the genus Alveolites is defined as follows (vol. ii. p. 285) : — 



" Corallum stony, sometimes incrusting, sometimes free and 

 massive, formed of numerous layers which are coneentiically su- 

 perimposed upon one another, each layer composed of tubular, 

 alveolar, prismatic cellules, which are somewhat short, and form a 

 network on the surface." Four species of the genus were recog- 

 nized by Lamarck, of which A. suhorbicularis and A escharoides 

 have been subsequently united with one another. A. madreporacea 

 is stated by Milne-Edwards to be a Pocillopora ; and A. incrustans 

 appears to be a Polyzoon. To the above four species Milne- 

 Edwards added, in the work just quoted, four others, of which 



