148 DR. SCHULTZE, ON THE RHIZOPODA. 



of calcareous salts. The only two marine genera in which the 

 shell is flexible are Gromia and Lagynis, in which it would 

 seem to resemble that oi Arcella, Euglypha, and Trinema. In 

 chemical constitution it approaches ddtin. The flexible shell 

 of these genera and of their fresh-water allies have but one 

 opening, and are not furnished with the minute pores which 

 are found so generally in the calcareous-shelled Rhizopods. 

 All the other Foraminifera are characterised by having a rigid 

 calcareous shell ; though there seems to be, at any rate, one 

 exception to this, in a new species described by Dr. Schultze, 

 under the name of Polymorphina silicea, in which the shell is 

 constituted of minute granules and angular tables of silex, and 

 which might, therefore, be compared with that of Difflugia. 



When recent Foraminifera are dissolved in dilute acid, an 

 organic basis is always left after the removal of the calcareous 

 matter, accurately retaining the form of the shell, with all its 

 openings and pores. The earthy constituent is mainly car- 

 bonate of lime ; but Dr. Schultze has satisfied himself of the 

 presence of a minute amount of phosphate of lime in the 

 shells of recent Orhiculina adunca from the Antilles, and of 

 Polystomella strigilata from the Adriatic. 



As respects the intimate structure of the shell, the calca- 

 reous Foraminifera may be arranged in two series ; in one of 

 which the shell is perforated by numerous minute openings or 

 canals, and in the other appears to be solid and homogeneous. 

 In the latter the animal communicates with the external world, 

 either through a single large opening, or, instead of that, there 

 may be several smaller openings grouped together. 



Dr. Schultze has never been able to detect any trace of an 

 organic envelope on the surface of the shell, as described by 

 Carter in Operculina arabica. 



The chambers of the shell communicate by similar pores 

 and canals through the dissepiments ; but of the " interseptal 

 spaces" described by Carter in Operculina arabica, and by 

 Williamson in a species of Faujasina (neither of which forms 

 had come under his observation). Dr. Schultze has never 

 seen any appearance in other Polythalamia belonging to nu- 

 merous genera. 



With respect to the classification of the Polythalamia, Dr. 

 Schultze takes the mode of disposition of the chambers as the 

 basis of his arrangement. Three principal types are in this 

 way afforded, according as the chambers are disposed in a 

 straight (or slightly curved) line ; or in a spi?-al direction ; or 

 in confused heaps. The first corresponding with the Stichoste- 

 giens of D'Orbigny ; the second with his Stelicostegiens, 

 Entomostegiens, Erallostegiens, and Agathistegiens ; and the 



