Hyatt.] 166 [Dec. 3, 



lenticular; in the female, however, this eminence is divided into three 

 minute points, which together are of the same size as the single ele- 

 vation of the male; this seems to show that the male ocellus is formed 

 of three elements united. 



In all the heterocerous Lepidoptera which possess ocelli, these are 

 two in number, and are placed one behind each antenna, probably 

 therefore on the vertex. This difference is not extraordinary, for 

 among the Hemiptera some groups possess ocelli below, some 

 above the eyes, a* difference still greater; while in other groups 

 they are wholly wanting. In the genus Larema, to which Papilio 

 Accius Sm.-Abb. belongs, two other species have been examined, L. 

 Pattenii and L. Hianna. In the male of the former (the only sex 

 examined) the ocellus resembles perfectly that of X. Accius; but there 

 is not the slightest trace of ocelli either in the male or female of the 

 latter; nor do they exist in the neighboring genera, so far as these 

 have been examined. 



December 3, 1873. 

 The President in the chair. Fifty-five persons present. 

 The following papers were read : — 



Evolution of the Arietid^e. By A. Hyatt. 



My researches continued during the past fourteen years upon the 

 Ammonites of the Jura, but. more especially upon the family of Arie- 

 tidse, have led to the following results. 



The parent form of the family, which includes the genus or group 

 Arietes, of Von Buch, and the series to which Scipionianus belongs, 1 



1 Tliis, however, does not include the group of Amm. angulatus, Charmassei, 

 Leigneletii and Boucaultianus. These, hy their young and adult forms, are dis- 

 tinctly separable from any of the true Arietian forms. The young have a stout, 

 smooth whorl, followed by a stage in which the ribs are developed, and pass con- 

 tinuously over the abdomen. In the next stage the sides become flatter, the ribs 

 on the abdomen divided by a channel, and in all the forms except angulatus or 

 catenatus, the involution is notably increased. In the first old age stage the ribs 

 again become confluent on the abdomen, and in the last stages almost or entirely 

 obsolete. This stage compares in form and all its characteristics, with Boucaultia- 

 nus, the last representative of this special series. 



Catenatus and angulatus occur at Lemur with tortilis immediately above planor- 

 bis, and below the Angulatusbed. Angulatus with Charmassei and Leigneletii in 

 the Angulatusbed, Charmassei continuing on into the Bucklandibed, succeeded 

 by Boucaultianus in the Tuberculatusbed of Oppel. 



