116 BULLETIN 77, "UNITED STATES ISTATIONAL MUSEUM. 



ESCHAROPORA SUBRECTA (Ulrich). 

 Text fig. 44. 



Ptilodictya subrecta Ulrich, Fourteenth Arm. Rep. Geol. Nat. Hist. Surv. 



Minnesota, 1886, p. 63; Geol. and Nat. Hist Surv. Minnesota, vol. 3, pt. 1, 



1893, p. 168, pi. 12, figs. 5-29. 

 Cfr. Micropom rhombica Eichwald, Lethsea Rossica, vol. 1, 1860, p. 395. 



The only species of Escharopora recognized in the Baltic strata is 

 represented by a number of well preserved examples from the Wassa- 

 lem beds (D3) at Uxnorm. These agree in all their characters and 

 show the same range of variation as the abundant American form 

 E. subrecta, the types of which are before me for comparison. Ulrich 

 has given a very detailed and careful description of the species and 

 has illustrated it most fully in his third volume of the Mimiesota 

 reports. Certain of his figures are exactly duplicated in the Rus- 

 sian specimens, and these have been selected for illustrating the 

 species at the present time. 



The zoarium is usually a simple, smooth, bifoliate expansion with 

 the lower portion gradually tapering to a pointed, articulating, finely 

 striated basal extremity, as shown in figures 44 a and I. Older speci- 

 mens may reach the size shown in figures 44 d and e, and, as in the 

 latter, somewhat inconspicuous monticules may be developed. The 

 finely striated basal portion is composed of elongated groove-like 

 spaces which become wider further up in the zoarium and gradually 

 change into the elongate confluent zooecial aperture characteristic 

 of the species. This change is illustrated in figure 44 h, and the 

 usual aspect and arrangement of the aperture is shown in -figure 44 c. 



Measuring lengthwise there are about 11 apertures in 5 mm. and 

 diagonally 9 to 10 in half that distance. Six of the central rows 

 occur in 1 mm., measuring transversely. As indicated in several of 

 the figures, the walls frequently fail to join and thus leave narrow 

 channels between the apertiu^es. In old examples, such as shown in 

 figure 44 e, these channels are sometimes replaced by mesopores (fig. 

 44/), giving a less regular arrangement to the zocecia. 



The two sections reproduced in figures 44 g and Ti exhibit the 

 internal structure clearly enough to make its detailed description 

 unnecessary. However, the long, primitive cell in tangential section 

 and the slight development of hemisepta as shown in the vertical, are 

 to be noted. 



The simple, pointed, bifoliate zoarium and the elongate, somewhat 

 confluent, diagonally arranged zocecia of Escharopora subrecta are so 

 unlike any associated Russian forms that comparisons are hardly 

 needed. The pointed base is usually preserved and this alone gives 

 a good clue to the species. Other bifoliate species with pointed 

 bases, such as Graptodictya proava have a quite different zoarium. 



