228 Mr. II. (J. Smith on Tim 



Iiitonnediatc variafioii.-* may be indicated 1)V tlic use, of 

 dashes beside the fiij^uves. 



Thus we may represent the different series as follows: — 



>S. flirhofovia series. 



p. c. I. r. 



S. (Uchotomn (Lamx.) 2 1 1 Jurassic. 



»S. ffranulata, M.-Edw. (non auct.) 2' 0' 1 1 Cretaceous. 



S. cUvaricata, Reuss 2' 0' 1' 0" Miocene. 



S. trahensy Couch {S. granulata, 



Johnst.) 2" 0" 1 2 Recent. 



S. dichotomoides series. 



p. c. I. r. 



S. dichotomoides (d'Orb.) 1 2 1 Jurassic. 



5. plicata, d'Orb 1 2' 1 Cretaceous. (Or- 

 namentation differs.) 

 <S. vesiculosa (Mich.) 1 2" ] Miocene. 



S. Walt on i series. 



p. c. I. r. 



S. Waltoni , HfdmQ 1 2 Jurassic. 



S. longiscata, d'Orb 1" 2 Cretaceous. 



S. Retissi, n. nom.* 2 2 Miocene. 



Eacli of these three sets of formulse shows a gradual increase 

 in the degree of development of the distinguisliing cha- 

 racters. This fact is clearly brought out by the formula3. In 

 some species the later types, however, are simpler than tlieir 

 Cretaceous representatives, for the genus attained its maximum 

 in the Mesozoic, and has been on the wane throughout the 

 Cainozoic. The different stages may be called either species 

 or varieties. It probably does not matter which name is 

 adopted, so long as the differences between them are marked 

 and the forms grouped together in series round the best- 

 known type. 



XXVII. — Descriptions of Two neio Species of Pieridaj cap- 

 tured by Captains Cayley Webster and Cotton in JVew 

 Georgia, Solomon Islands. By H. Grose Smith. 



Deltas georgiana. 



Male. — Upperside. Anterior wings white, with the costal 

 margin, costal and subcostal nervures black ; the third sub- 



* Aulopora divaricata, Reuss (non Roenier), Foss. Polyp. Wien. Tert. 

 1847, p. 53, pi. vii. fig. 18. 



