258 ME. J. W. GEEGOKY ON THE 



Figures. PL XXXII. figs. 2 a, '2,1. Zoaiium and section. 



Affinities. This species belongs to the first of the groups of Idmonea, including 

 those with the zooecia all in lateral series. It most closely resembles a specimen 

 figured by Manzoni [No. 4, p. 5, pi. iii. fig. 10] as 1. carmata%, Rom. A comparison 

 with the figures both of Eomer [No. i, p. 21, pi. v. fig. 20] and Reuss [No. i, pp. 44, 45, 

 pi. vi. fig. 27] would seem to show that the query after the identification was very well 

 founded ; in the number of zooecia, the shape and structure of cross-sections, and other 

 points, Manzoni's figures markedly difiier from those of the larger pluriserial triangular 

 species figured by Romer from the North-German Chalk. From the typical /. carinata 

 the Loudon Clay species can be very readily distinguished. 



Idmonea reticulata, Reuss [No. 11, pp. 281, 282, pi. xxxiv. fig. 13], belongs to the 

 same series, but diffiers in the smaller size and more regular arrangement of the zooecia 

 and apertures, which are grouped in triplets instead of pairs. The same characters also 

 separate the new species from the /. laticosta. Mars. [No. i, p. 29, pi. ii. fig. 11], of 

 Danian age, which belongs to the same group. 



Species 3. Idmonea seriatopoba, Reuss ("?). 



Syn. Idmonea seriatopora, Reuss, 1847, Foss. Polyp. Wiener Tertiarbeckens, p. 46, pi. vi. fig. 33; 

 Manzoni, 1878, Brioz. foss. Mice. Austr. Ungh., Denk. k. Ak. Wiss. Wien, Bd. xxxviii. 

 Abth. 2, p. 6, pi. vi. fig. 12. 



Diagnosis. Zoarium of thick irregular branches, composed of many zooecia, well 

 rounded at the back. 



Zooecia very irregularly arranged, the lateral ones the longest. There are no regular 

 series arranged on either side of a medial line. Three zooecia often open in an oblique 

 line. 



Peristome elliptic ; border irregular. 



Distribution. London Clay, Haverstock Hill. — Foreign. Leithakalk (Helvetian), 

 Austria. 



Ti/pe. Brit. Mus. No. B 4510. 



Figures. PI. XXXII. fig. 4 a. Part of a zoarium, X 18 diam. Fig. 4 b. Mouth, 

 X 32 diam. Fig. 4 c. Transverse section, X 18 diam. Fig. 5. Back view of zoarium. 



This species belongs to the subgenus Tervia of JuUien. 



Affinities. The irregular distribution of the zooecia of this species reminds one of 

 I. compressa, Reuss [No. i, p. 46, pi. vi. fig. 22], but the zoarium is not so laterally 

 compressed. Its closest ally is Idmonea seriatopora, Reuss, as figured by Manzoni 

 [No. 4, pp. 6, 7, pi. ii. fig. 8, pi. V. fig. 17] ; to the original and no doubt 

 diagrammatic figure of Reuss it has a less decided resemblance. But the London Clay 

 specimen is not sufficiently large to allow of a more definite comparison ; hence I do 

 not feel able positively to affirm the occurrence of the Austrian Miocene species in the 



