BRYOZOAK FAUNA OF VINCENTOWN LIMESAND 31 



1862. Membranipora abortiva Gabb and Horn, Ibid., p. 157, pi. 20, fig. 41. 

 1907. Flustrellu capistrata Ulbich and Bassler, in Weller, Geol. Surv. New 

 Jersey, Paleontology, vol. 4, p. 329, pi. 22, figs. 5, 6 (bibliography). 



Description. — In Membranipora abortiva Gabb and Horn, the 

 zoarium encrusts fragments of shells and other Bryozoa. The 

 zooecia are distinct, separated by a deep furrow, elongated, elliptical, 

 with a short convex gymnocyst; the mural rim is salient, thin, 

 smooth, bearing 1 or 2 pairs of spines; the cryptocyst is shallow, 

 short, concave, enlarged at the base. The opesium is elongated, pyri- 

 form. The ovicell is hyperstomial, never closed by the operculum, 

 globular, smooth or decorated with two crescents arranged sym- 

 metrically. There is an auriform vibraculum (?) in each angle of 

 junction of the zooecia. The ancestrula is a small ordinary zooecium. 

 The aborted zooecia are irregular, convex, smooth, deprived of mural 

 rim, perforated by a small median orifice. 



Measuremen ts . — 



. [Lz= 0.3-0.4 mm. ~ \ho = 0.15-0.17 mm. 



Zooecia^ , _ _ (JpesmnU 7 _ 10 A . , 



|fe=0.2 mm. r [ Jo = 0.12-0.14 mm. 



45 zooecia in 4 sq. mm. 



/Structure. — This is a curious and complicated species, the biology 

 of which and the nature of the small intercellular organs are difficult 

 to interpret. We believe the latter are auriform vibracula, although 

 they have been interpreted previously as avicularia. The discovery 

 of specimens with perfect preservation could only solve the question. 

 Moreover, it would be only by the discovery of a basal side that we 

 could learn whether they are interzooecial. They are arranged 

 longitudinally, and their orifice is oblique with respect to the zoo- 

 ecial plane. Their presence is constant, and their absence occasions 

 the regeneration of adjacent zooecia. 



Each new zooecial series begins always with a vibraculum, but 

 it is turned inversely to the adjacent vibracula. Because of the 

 slight zooecial length it is placed just above the normal vibraculum 

 dependent on the proximal zooecia and almost adjacent to the vibrac- 

 ulum of the distal zooecia. As a result each new zooecial series 

 appears to commence with a small chain of three or four vibracula. 



In the ancestrular region, the zooecia are deprived of interzooecial 

 vibracula; those which form are always primoserial and conse- 

 quently they do not have the chain formation mentioned above. 



The specific character is the presence of the peculiar aborted 

 cells. Without normal orifice they cannot contain a polypide. 

 Without mural rim they have simply the aspect of calcareous vesi- 

 cles variable in dimension and form. They are sporadic or in 

 groups. They much interested Gabb and Horn, who described them 

 as follows : 



