NOTES ON RETICULARIAN RHIZOPODA. 57 



rounded. Segments about nine in each convolution. Septa 

 marked by more or less sinuate lines, only slightly de- 

 pressed. Exterior smooth, usually polished ; interior surface 

 often reticulate; colour brown. Aperture crescentic, 

 situate on the face of the terminal chamber, close to the 

 margin of the previous convolution. Diameter ^V inch 

 (1-25 mm). 



The first examples of this beautiful little shell that came 

 under my notice were in the Rev. A. M. Norman's mountings 

 from the "Valorous" dredgings in Davis' Straits, but the 

 " Challenger " material has yielded a supply of specimens 

 from a number of localities. Trochammina trullissata is easily 

 distinguished from any other species by its perfectly regular, 

 nautiloid, or Nonionine contour, the number of chambers in 

 each whorl, their sigmoid sutural lines, and its polished 

 brown exterior. It is not unlike the very large nautiloid 

 type, Cyclammina, in its general conformation, but 

 differs widely from it in point of size and internal struc- 

 ture. The inner surface of the test of Tr. trullissata some- 

 times exhibits a slightly raised reticulation, but this in no 

 case, so far as my observation goes, is more than a mere 

 superficial marking, and never comes to anything re- 

 sembling the cancellated shelly growths that often nearly 

 fill the chambers of Cyclammina. 



The distribution of the species is wide, but it is by no 

 means abundant in any locality. The best " Challenger '^ 

 specimens are from two stations in the North Atlantic and 

 two in the South Atlantic, the depth of water varying from 

 390 to 2200 fathoms. 



Trochammina ringens, n. sp} PI. V, fig. 12, a, h. 



Characters. — Test nautiloid, oblong, compressed, biconvex; 

 composed of few convolutions, of which the last entirely en- 

 closes the previous ones. Peripheral margin acute-angular, 

 or slightly rounded, lobulate j septal lines curved, somewhat 

 excavated. Segments large, about five in each convolution, 

 embracing. Colour brown, surface usually polished. Aper- 

 ture an arcuate slit, overhung by a slight swellitig or pro- 

 minence on the face of the terminal chamber, and near the 

 margin of the previous convolution. Longer diameter -^ inch 

 (1*25 mm.). 



' This form was recorded by Mr. Norman, in the " Valorous" Report 

 (' Proc. Royal Soc.,' xxv, 1876, p. 213), as "very near to, if not identical 

 with, Globigerina arenaria, Karrer," but he has subsequently received types 

 of that species from Dr. Karrer, and is now sutisficd of llieir entire uis- 

 tinctness. 



