368 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



of Australia there is a great development of Baculogypsina sphaeru- 

 latus as shown in the series of samples collected by Dr. Alfred G. 

 Mayor on the Carnegie Expedition to Murray Island. This species 

 makes up a large proportion of the material and Siderolites is en- 

 tirely lacking. Baculogypsina sphaerulatus is abundant at the Atoll 

 in Funafuti according to Chapman, but no figures or mention is made 

 of the other. The more detailed distribution of these two genera and 

 their relations to the Eocene would be interesting. 



From their development, Calcarina, with its close-coiled test, rep- 

 resents the simplest form, and in its geological history apparently 

 goes back to the Cretaceous. Siderolites is the next in order, the 

 close-coiled spiral development being continued for sometime in the 

 young before the later method of growth is attained. This goes 

 back geologically to the Cretaceous. Baculogypsina as applied here 

 has a very short-coiled stage in the very young and then assumes the 

 generic character. Thus a much more accelerated development is 

 shown and a higher position in the scale. The supplementary skele- 

 ton of bosses and radial connections is also carried to a high develop- 

 ment, making a firm test, whereas Siderolites is fragile as far as the 

 chambers are concerned (pi. 45, fig. 4) . 



EXPLANATION OF PLATES. 

 PLATB 44. 



FIG. 1. Calcarina spengleri (Gmelin) ventral view. X 20. 



2. Calcarina defrancii d'Orbigny ventral view X 20. 



3. Calcarina baculatus ( ?) (Montfort) ventral view. X 20. 



4. Calcarina hispida H. B. Brady ventral view. X 20. 



5. Siderolites tetraedra (Giimbel). X 15. 



6. Baculogypsina sphaerulatus (Parker and Jones). X 20. 



PLATE 45. 



PIGS. 1-5. Siderolites (?) tetraedra (Giimbel). 



1. Young, -ventral view. X 45. 



2. Later stage, chambers invading dorsal side. X 40. 

 a, ventral side ; 6, dorsal side. 



3. Still later stage where dorsal side is partly covered by the invading chambers. 



X 35. 

 o, ventral side; b, dorsal side. 



4. Old eroded specimen, in which the chambers are largely broken away leaving 



the raised bosses (x) as projections from the center. X 18. 



5. Specimens in which the chambers now cover even the spines. X 15. 



O 



