352 CUMINGS AND GALLOWAY MORPHOLOGY OF TREPOSTOMATA 



The proximal portion of tlie brown mass rests usually on a well defined 

 diaphragm, and the mass itself occupies the space between the cysti- 

 phragms and the opposite wall of the zooecium. Often near the top of 

 the brown mass the cystipliragms line the zocecial tube all the way round, 

 so that the constricted space left between them forms a narrow neck. 

 Tangential sections show that this neck is usually of tubular cross-section. 

 A short distance above (distally to) this neck there is another well de- 

 fined diaphragm, and above the latter diaphragm, in turn, there often 

 appears (in Peronopora usually) another brown mass, with a repetition 

 of the succession of cystiphragms, etcetera, as just described. 



The arrangement of cystiphragms and diaphragms, just described, 

 characterizes the Monticuliporidse, in which cystiphragms are a normal 

 feature. A precisely similar arrangement is sometimes seen in Batostoma 

 (figure 10) and in Heterofi ypa (figures 2 and 6). The relative posi- 

 tions of brown mass, cystiphragms, and diaphragms are identical. In 

 these latter genera, however, the brown mass is usually surrounded by a 

 well defined calcareous cyst, of which the typical cystiphragms constitute 

 only the neck region (figures 3, 4, 5, 7, 11, and 14). Other figures show 

 various arrangements intermediate between the two. In some cases the 

 proximal end of the cyst is separated more or less from the basal dia- 

 phragm {d' of the figures). This is shown in figures 1, 3, and 7. 



The neck of the cyst is nearly always clear and free from the brown 

 material. It may be open above — that is, with a considerable clear space 

 between it and the distal diaphragm (figures 2, 4, 14, etcetera) — or it 

 may be securely stoppered l)y a diaphragm of greater or less thickness 

 (figures 1, 9, 11, etcetera). Occasionally the neck contains foreign parti- 

 cles that can be very easily distinguished from the peculiar brown ma- 

 terial. As shown in a number of the figures, the wall of the cyst is con- 

 tinuous, distally, with the inner tenuous lining wall of the zooecium. 

 Tlie space between the cystiphragms and the main zocecial wall, or be- 

 tween the neck of the cyst and the wall, is absolutely empty, never show- 

 iyg anything but clear, well crystallized calcite, with which it has, of 

 course, become infiltrated during fossilization. That this space was 

 originally merely a void between the endosarc of the polypide and the 

 interzooecial wall is certain. 



The nature of the brown material is as suggestive as its position and 

 relations to surrounding structures. It consists of minute rounded par- 

 ticles from a seventy-fifth to a hundredtli of a millimeter in diameter, of 

 a dark yellowish brown color, as seen by transmitted light, and marked 

 by lighter bands, as shown in figure 31. These particles consist of 



