WALL STRUCTURE 359 



believe that wall structure, properly understood, will prove important in 

 generic and family classification within this order. This idea was empha- 

 sized by Ciimino-s in his paper on the Heterotrypidse (6). In their re- 

 vision of the Trepostomata, Ulrich and Bassler (35), on the basis of wall 

 structure, divided the order into two divisions: the Amalgamate, in 

 which "the boundaries of adjacent zotpcia are obscured by the more or 

 less complete amalgamation of their walls,'' and the Integrata, in which 

 "the bouiidf!,rieR of adjoining zocecia are sbai'plv defined by a well-marked, 

 ostomaict. ] divisioiinl lino" (34). 

 Deliayia, 1 

 convince an fsroLOor of the walls and the median line 



direct y iroi aiTfu^^gejYigi-i^; ^f the Trepostomata seemed to the writers to 

 as seen m :^^^ ^^^^ ^^^^^^ iiseful. The first to express any dissatisfac- 

 an( gur < -^ (18), who noted that a dark line was occasionally 

 \eise y o jgQJgg otherwise referable to the Amalgamata. Our atten- 



PL O 



specime \)een called to this same fact in certain species of Hetero- 



gmia, -mc } |.yp j^g^j member of the Amalgamata. It presently occurred 

 1'*^'^ a careful restudy of the histology of the trepostome walls 



ne - P / ' ligher magnification than has hitherto been employed and 

 „ \\ rather than in tangential sections, since the actual course 

 '^^^ 'iminas from face to face of the wall can not be folloAved in 



f"^d of section. The results of these studies are shown in fig- 

 ^ ' •' , inclusive. Figure 45 shows the median line in its sharpest 



/^.ppears in Batostoma vnnchelli, while figures 42, 48, and 50 

 ^ . typical amalgamate structure as it appears in Bythopora, 

 ^ ^v,ypa, and Dekayia. These two types of structure certainly ap- 

 pear to be very distinct; nevertheless both may and do occur in the same 

 species, and indeed in a single specimen. Figures 46 and 47 are sections 

 of Heterotrypa prcenuntia, both from the mature region. Figure 43 

 shows the amalgamate phase of structure in Amplexopora septosa mul- 

 iispinosa, a member of the Integrata, while figure 48 shows it in Hetero- 

 trypa proUfica, a typical member of the Amalgamata. There is no real 

 difference between these two walls. It is very rarely indeed that the ap- 

 parently sharp divisional line of the wall is not resolved by high magnifi- 

 cation into an irregular zone, such as is shown in various phases in figures 

 43, 49, and 5(;. Figure 40 is instructive, since Eridolrypa is regarded as 

 a member of the .\malgamata. It may with profit be compared with 

 figure 45. Tlic ivw meaning of this dark zone is revealed by comparison 

 of figures 56 and 'u. These sections are cut in portions of zoaria where 

 *he zoarial surface has been perfectly preserved by overgrowth. The 

 ^TOwing edge of the wall is shown intact. In figure 56 {Hallopora 



^ XXVI — Bull. Geol. Soc. Am., Vol. 26, 1914 



