230 MK. J. W. GEEGORT ON THE 



Omcia triangular : surrounded by a rim like that around the zocecia. 

 Avicularia sparsely and irregularly scattered over the zoarium : occupying the 

 small triangular areas between the zocecial margins. 



The raised rim is usually plain, but may bear a single minute tubercle, the base of a 



small spine. 



Distribution. Barton Beds, Barton. Bracklesham Beds, Bracklesham. 



Ti/pe. Brit. Mus. No. 49741. 



Figures. PI. XXIX. fig. 10 a. From Barton. Several zocecia, showing the ooecia, 

 avicularia, bases of spines, and lamina. Fig. 10 b. Another specimen, growing on a 

 strongly ribbed Pecten. 



Eemarks. This species appears to be most closely related to that figured by 

 Reuss [No. 14, p. 179, pi. ix. figs. 1, 2] as Memhranipora elliptica (Hag.) from the 

 Leithakalk (Helvetian) of Eisenstadt. But the London Clay species appears to be 

 certainly distinct from that represented in von Hagenow's original figui-e [No. i, p. 268, 

 pi. iv. fio'. 6], in which the rims surround the area instead of the zocecia and thus 

 are separated by a wide space, both in the centre and youngest part of the zoarium ; 

 there are neither laminae nor ooecia. Hagenow remarks on the " vertiefteu Zwischen- 

 raumen " with ring-shaped pores. But as to the identity of M. crassomuralis with 

 the Eisenstadt species I do not care to express a definite opinion without seeing 

 Reuss's type. Pergens [No. 1, pp. 15, 16] seems to have entertained the same 

 doubts as to the correctness of Reuss's identification, for though he quotes M. elliptica 

 from the Austro-Hungarian Miocenes, he does not include Reuss's reference in his 



synonymy. 



This species belongs to the M. lacroixi group, but it differs in the following characters : 

 (1) it has triangular ooecia, whereas these structures are said by Hincks [No. 2, p. 130] 

 to be absent in the recent species ; (2) the rim is not crenulate ; (-3) the avicularia are 

 fewer, and there is never more than one spine on the rim. 



From Memhranipora eocena (Busk) it differs in the absence of any space below the 

 area and outside the rim, and also of the two small lateral avicularia ; the zocecia are 

 also arranged more irregularly. 



Memhranipora temporaria, Waters [No. 6, p. 288, pi. vii. fig. 16], from the Murray 

 River cliffs, is an allied species, but differs in the presence of two small lateral avicularia 

 and a larger " infra-area." 



Another species with which this new one must be compared is Memhranipora 

 loxopora (Reuss) [No. 2, p. 166, pi. viii. fig. 11 : for later figures see No. 14, pp. 39- 

 40, pi. ix. figs. 4, 5 ; the author's original figure in No. 1, p. 97, pi. xi. tig. 24, 

 has been subsequently repudiated by him], but this has larger front walls, on which the 

 avicularia are placed, instead of in the angles. 



Reuss [No. 13, p. 101, pi. xxiv. figs. 4 & 5 c] has himself also figured the typical 

 Cretaceous M. elliptica from the Unter Planer of Saxony, and one of his figures shows 



