. Bulletin - United States National Museum. Science. 304 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. DITTOPORA ANNTJLATA (Eichwald). Plate 3, fig. 5; plate 11, figs. 16, 17; text figs. 186, 187. Chaetetes annulatus Eichwald, Lethaea Rossica, vol. 1, sect. 1, 1860, p. 480, pi. 28, figs. 2a-2c, 3a-3d. DiWopora anntiZaia Dybowski, Die Chaetetiden derOstbaltischen Silur-Formation, 1877, p. 86, pi. 2, fig. 5.—Nicholson, The GenusMonticulipora, 1881, p. 234, fig. 49. Zoarium of small, ramose, frequently dividing branches 3 to 6 mm. in diameter. Surface finely spinulose on account of the numerous sma
. Bulletin - United States National Museum. Science. 304 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. DITTOPORA ANNTJLATA (Eichwald). Plate 3, fig. 5; plate 11, figs. 16, 17; text figs. 186, 187. Chaetetes annulatus Eichwald, Lethaea Rossica, vol. 1, sect. 1, 1860, p. 480, pi. 28, figs. 2a-2c, 3a-3d. DiWopora anntiZaia Dybowski, Die Chaetetiden derOstbaltischen Silur-Formation, 1877, p. 86, pi. 2, fig. 5.—Nicholson, The GenusMonticulipora, 1881, p. 234, fig. 49. Zoarium of small, ramose, frequently dividing branches 3 to 6 mm. in diameter. Surface finely spinulose on account of the numerous small acanthopores; maculas of thick-walled mesopores usually closed at the surface, and encirchng the branch, giving the character- istic annulated appearance. In the early portion of the mature region the usual pair of larger acanthopores, one on each side of a. Fig. 186.—DiTTOPOEA ANITOLATA. copy of ElCffWALD'S ILLTTSTEATIONS OF CiLETETES ANNT7LATU3. B, FRAGMENT OF A NORMAL MATURE ZOARIUM, NATURAL SIZE; 6, SMALL PORTION OF THE SAME MAGNIFIED TO SHOW THE ARRANGEMENT OF THE RING-LIKE MACULE AND THE DISTRIBUTION OF ZOCECIA AND MESO- PORES; C, END VIEW OF A FRAGMENT ENLARGED; d, VIEW OF CELLS IN SECTION; € AND/, FRAGMENT OP AN OLD EXAMPLE AND A PORTION ENLARGED. HERE THE ZOCECIA ARE ALMOST ENTIRELY OBLITERATED BY THE EXTENSIVE DEVELOPMENT OF MESOPORE-LIKE CELLS; Q, END VIEW OF BRANCH, MAGNIFIED. "CaLCAIRE 1 OETHOCERATITES," PULKOWA and PoPOWKA, GOVERNMENT OF ST. PETEESBUEG. zooecium, is present, but numerous smaller acanthopores develop in the later portions of the same zone and become so nearly equal in size that the distinction between the two sets is lost. The tangential sections shown in figure 187 a and & are through this older portion of the mature region. Dybowski's figure (pi. 3, fig. 5) represents the larger set more distinctly, and also shows the hour-glass shape imparted to the zocBcia by the indentations of the walls whenever a pair is well developed
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