204 CRETACEOUS PALEONTOLOGY. 



curving irregular chain; chambers attached by stoloniferous 

 tubes; aperture terminal in ultimate chamber; length variable, 

 dependent upon the number of chambers. 



"Breadth, 0.2-0.6 mm. ; shell diameter, o.oi mm." (Bagg.) 



Remarks. "This is a very common form at Vincentown, and 

 is frequently found adhering to Flabellina sagittaria, 'although 

 often occurring on other shell fragments. Although the pri- 

 mordial chamber is generally the smallest and the ultimate the 

 largest, there is no regularity of arrangement in regard to size of 

 the chambers. 



"It was with some difficulty that the position of this form was 

 determined. The structure of the shell substance alone separates 

 it from Trochammina irregularis Carpenter, 1 but solution of the 

 shell in hydrochloric acid failed to reveal any trace of arenaceous 

 or siliceous material, although in some cases there was an inner 

 coating of amorphous material remaining insoluble in the acid. 



"A form similar to the one under discussion is figured by 

 Quenstedt 2 and described by him as Bullopora rostrata in the fol- 

 lowing words : 'This consists of simple, small, dark hemispheres, 

 united with each other through lengthened tubes. This tube 

 often projects from the end cell like a beak, whence I have given 

 it its name. Generally the pustules (chambers) increase in size, 

 with now and then smaller ones between, while the primordial 

 cell is similar to those succeeding.' This species is described by 

 Schwager 3 as Placopsilina rostrata, and is placed under the cal- 

 careous perforate division of the Dentaloidea. 



"In the original description of the genus Placopsilina 4 no men- 

 tion is made of the nature of the test, whether of arenaceous or 

 calcareous composition, but later authorities (Brady 5 ) consider 

 the genus under arenaceous types of the Lituolidse. 



"The tubulated structure of the genus Webbina, simulating the 

 arenaceous Trochamminse, is quite striking, and its calcareous 



1 Introduction to the Study of the Foraminifera, p. 142, PI. XI, figs. 6-10. 



2 Der Jura, 1858, p. 580, Atlas, PI. LXXIII, fig. 28. 



3 Bolletino del R. Comitato Geol. d'ltalia, 1877, vol. viii, p. 18, PI. fig. 12. 

 M'Orbigny, A. D., Prodrome de Paleontologie Stratigraphique, 1850, vol. ii, 



p. 96. 



5 Challenger Report, 1884, vol. ix, p. 314. 



