LINNE.VN SOCIETY OF T-OXDON. 



8.3 



in almost every case, be made out with ease by a careful examina- 

 tion of the ventral surface of the vertebral column (see text- 

 figure). In a few specimens in the Collection of the British 

 Museum the vertebrae were sufficiently free to admit of an actual 

 observation of the anterior faces of the sacral and preceding 

 vertebrae. In every such case this examination confirmed the 

 opinion already formed from the examination of the entire 

 vertebral column of a specimen of the species in question. A 

 few specimens (a bare half-dozen), concerning which I could not 

 feel absolutely certain, were referred to Mr. Boulenger, who was 

 able to confirm, in every case, the correctness of the conclusion at 

 which I had, provisionally, arrived. 



The result of this investigarion was quite unexpected, for, as 

 has been shown, it was found that the Diplasiocoelous (" pro- 

 coelous ") condition, which was supposed to characterize " the 

 overwhelming majority" of Anura, is in fact confined to the 

 i^'irmisteruial forms I 



Ventraf view of the liiiider part of the vertebral columns of (A) Disc.oglossits 

 piotus, (B) Pclubatcs JmciDi, (C) Bic/o aiidersoiiii (all X 2), and (D) Rcma 

 tigrina (nat. size), to show the opistbocoelous, auouiocoelous, proccelous, 

 and diplasiocoelous conditions. 



The biconvexity of the centrum of the sacral vertebra, there- 

 fore, so far from being an " invariable " feature of the Anuran 

 vertebral column, is in fact restricted, except for individual 

 variation, practically to the Discoglossidae and the Firmisternia *. 



On the other hand, a vertebral column in which all the centra 

 are hollow in front (Proccelous, strictu sensu) is found in the 

 Cystignathidoe, Hylidae, Bufonidae, and the Pelobafidae, i. <?., the 

 whole of the Arcifera excluding only the Discoglossidae. 



The PelobatidaB are known to be extremely variable in the con- 

 dition of the vertebral column. They are, nevertheless, excepting 



* A few opisthoccslous Pelobatidae may have a biconvex ninth centrum, 

 which is, however, easily distinguished from those of Discoglossidae or 

 Firmisternia by its single coccygeal condyle. 



