228 Mr. H. G. Smith on Two 



Intermediate variations may be indicated by the use of 

 dashes beside the fig-ures. 



Tlius we may represent the different series as follows : — 



S. dichotoma series. 



p. c. I. r. 



S. dichotoma (Lamx.) 2 I 1 Jurassic. 



/S. granulata, M.-Edw. (uon auct.) 2' 0' 1 1 Cretaceous. 



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



S. trahens, Couch («S'. granulata, 



Johnst.) 2" 0" 1 2 Recent. 



S. dichotomoides series. 



p. c. I. r. 



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



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

 namentation differs.) 

 S. vesicidosa (Mich.) 1 2" 1 Miocene. 



S. Waltoni series. 



p. c. I. r. 



S. Waltoni, Hainie 1 2 Jurassic. 



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



*S. Heussi, u. nom.* 2 2 Miocene. 



Eacli of these three sets of formulse sliows a gradual increase 

 in the degree of development of the distinguishing cha- 

 racters. This fact is clearly brouglit out by the formula}. 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 througliout 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 gi'ouped together in series round the best- 

 known type. 



XXVII. — Desa-iptions of Two new Species of Pieridse cap- 

 tured hy Captains CayJey Webster and Cotton in I^ew 

 Georgia, Solomon Islands. By H. Grose Smith. 



Delias georgiana. 



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

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



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

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



