^ ^ BRYOZOA. 171 



Kscharopora.] 



ESCHAROPORA CONPLUENS tl. Sp. 

 PLATE XIII, PIGS. 1-12. 



Zoarium branching, the smallest seen less than 25 mm. high, with the branches 

 averaging about 2.5 mm. in width ; the largest fragments indicate a bight of from 

 80 to 120 mm., and in these the width of the branches varies from 4 to 8 mm. The 

 two surfaces of the branches are generally obtusely ridge-shaped, and in the largest'a 

 row of monticules, or simply clusters of large cells, occurs on the summit of the 

 ridge. Edges thin and sharp, commonly with a coarsely striated or pitted narrow 

 border. Through all stages, though less distinct in the oldest, the zooecial apertures 

 are nart-ow and appear to be drawn out at the ends so as to connect by means of a 

 narrow channel. This confluent character of the zooecial apertures is better shown 

 and more regular in the central rows, where they are also narrower and on the 

 whole considerably smaller than toward the margins. (See fig. 5.) In the central 

 rows, ten in 5 mm. lengthwise ; eighteen or nineteen in 5 mm. diagonally, and five 

 and one-half in 1 mm., and ten in 2 mm. transversely ; of longitudinal rows there 

 are nineteen or twenty in 2 mm. 



Tangential sections show that the base of the zooecia, excepting those in the mar- 

 ginal rows, is bounded by very thin, straight, longitudinal walls, and equally thin 

 transverse partitions. This portion of the zocecium therefore may be described as 

 a parallelogram, with the length and breadth respectively as four is to one. At 

 about the middle of the hight of the primitive cell its sides have, spread a little and 

 the ends contracted in a corresponding degree. Just as the posterior half is about 

 to be roofed over two projections from the side walls, at a points a little behind the 

 middle, gradually converge until they meet and thereby cut off and enclose the ellip- 

 tical primitive aperture. In the succeeding stages the principal change is a reduc- 

 tion in the size of the apertures, caused by an internal deposit. These stages are all 

 shown in figs. 6, 7 arid 8, hut to insure a trustworthy idea of the internal structure 

 of the species, they should be studied in connection with figs. 10 and 11. 



Compared with associated Bryozoa, the next described E.{?) limitaria only will 

 be found difficult to distinguish. This, however, is due chiefly to the imperfect pre- 

 servation of the surface of most specimens. Good examples of the latter are quickly 

 distinguished by the different character of the longitudinal interspaces, these being 

 occupied by one elongated pit or two smaller ones. 



The zoarium of E. subrecta is always strictly of the simple type, and never 

 branches except under abnormal conditions. 



Specimens of this and the following species were catalogued by me in 1886 as 

 Ptilodidya ramosa Ulrich (now Escharopora ramosa)* Comparison with the Kentucky 



i^iwrteenth Aun. Eep. Geol. Nat. Hist. Surv. Minn., p. 102. 



