22 



BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



Another specimen with a larger megalospheric proloculum (fig. 28) 

 shows the following development. A large proloculum is followed by 

 a Cornuspira-like second chamber. Chambers 3 and 4 are arranged on 

 a quinqueloculine plan 144° apart, in the other megalospheric speci- 

 men represented by 8 chambers, and in the microspheric specimen 

 by 22. The triloculine stage is initiated by chamber 5 and the biloc- 

 uline by the eighth. 



Some of the very large megalospheric proloculi are followed in the 

 section directly by the biloculine stage, skipping entirely the quin- 

 queloculine and triloculine stages. 



Idalina and the other uniloculine genera with similar developmental 

 stages represent the height of development that it seems can be 

 reached along this line. Certain genera — Lacazina, for example — 

 may be more complex by the addition of labyrinthic partitions in the 

 interior of the chambers, similar to the labyrinthic interior of Fabu- 



laria, which is otherwise like Biloculina. 

 These uniloculine genera, then, bring to a 

 climax the progressive development of the 

 quinqueloculine group, and therefore the 

 highest type of development in the family 

 of the Miliolidae, with the exception pos- 

 sibly of the Peneroplis group, which in 

 many ways are different from all other 

 members of the family. 



Development of Peneroplis group. — The 

 fig. 28.— section of a specimen of development of typical specimens of Orbi- 

 ZZSJSS «; <™ **" ^d associated genera are considered 

 muniek-chalmas and schlum- under those genera in the sytematic por- 

 tion of the present paper and need not 

 be further considered here except that they have the proloculum and 

 Cornuspira-like second stage as in all other members of the family. 

 General lines of development. — From the preceding detailed descrip- 

 tions of the development seen in certain genera it will be seen that 

 the first two stages in all the members of the family, at least in the 

 microscopic form, consist of a proloculum and second chamber appar- 

 ently built by one continuous process and similar to the actual " em- 

 bryonic" young which have been actually seen in the parent tests in 

 several genera. Except for the length of the second chamber this 

 stage has the characters of an adult Cornuspira, therefore that genus 

 should be considered the basal member of the Miliolidae. 



Following Cornuspira there are a series of genera which, like Opthal- 

 midium, gradually assume division of the tube into chambers of de- 

 creasing length, following a long Cornuspira-like stage, and the cham- 

 bers all arranged in a planospiral manner. From here there are a 



