EAULY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 187 



as the mature region is approached these bend more and more until 

 they pass into the usual combination of cystiphragms and diaphragms 

 characteristic of the genus. In the mature region as many as five 

 cystiphragms may occur in a tube diameter, and often a double row 

 of these structures may be noted. In sections of old examples the 

 cystiphragms are observed to be obscured near the surface by a solid 

 filUng, which, with the gradually outward bend of the tubes and the 

 crowded cystiphragms and diaphragms, imparts a pecuHar aspect 

 to the species and makes it easy of recognition. 



Occurrence. — Not uncommon in the Wassalem beds (D3) at Ux- 

 norm, near Reval, Esthonia. In America the species is known 

 from the CHtambonites and Nematopora beds of the Lower Trenton 

 in Minnesota, Iowa, and Wisconsin, and at Ottawa, Canada. 



Plesiotype.—Csit. No. 57273, U.S.N.M. 



British Museum, specimens and one thin section of the Russian 

 type. 



HOMOTRYPA SUERAMOSA Ulrich. 



Text fig-s. 99, 100. 



Momoirypa subramosa Ulrich, Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. 

 Minnesota, 1886, p. 81; Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 

 1, 1893, p. 239, pi. 19, figs. 21-28; Zittel's Textbook of Paleontology (Eng. 

 ed.), 1896, p. 273, fig. 451 A-C (not I)=H. separata Ulrich). 



Several irregularly dividing subramose young specimens of Homo- 

 trypa from the Kuckers shale show all the surface characters of H. 

 subramosa, even to the shallow, zooecial apertures exposing the 

 cystiphragms. This similarity is borne out in the internal structure, 

 which, by comparison of the two sets of figures given here, allowing 

 for difference in the age of the specimens, may be seen to be identical. 

 Ulrich's description of the species is as follows: 



Zoarium subramose, frequently though irregularly divided; branches compressed 

 or Bubcyhndrical, their extremities often bulbous. Size of branches varying greatly, 

 the smallest 4 or 5 mm. in diameter, the largest 6 to 9 mm. thick, and as much as 25 

 mm. wide. Average specimens are about 6 mm. thick and between 8 and 12 mm. 

 wide, with the total height of zoarium rarely exceeding 60 mm. Surface without 

 monticules, nor a,re the clusters of large cells very conspicuous. Zocecia with rather 

 thin walls and polygonal, direct apertures; 12 to 14 in 3 mm. Zocecial apertures 

 shallow, exposing the cystiphragms when in a good state of preservation. These 

 structures leave but a small opening, and when the fossil has suffered a little from 

 attrition (a frequent occurrence in the beds holding the species most abundantly) in 

 which case the true walls are obscured or cut away, the appearance is very deceptive, 

 the apertures seeming to be very small and oblique, and much the greater part of 

 the surface occupied by wall substance. Acanthopores varying in number and 

 size, sometimes as numerous as two to each zooecium. More commonly the number 

 is little more than half that extreme. In many cases they are large enough to con- 

 stitute a marked external feature. In others, however, apparently in an equally 

 good state of preservation, they are so small that it is difficult to detect them even 

 with the aid of a good lens. 



92602°— Bull. 77—11 14 



