234 MR. J. W. GREGOET OX THE 



ancestmla. Fig. 2. Part of zoarium from Bracklesham (B 4-339), showing the front wall 

 partly broken away. Fig. 3. Part of a worn specimen from Bracklesham, resembling 

 L. urceolata. 



Affinities. This species belongs to the L. radiata, Lamk., group, which the Marquis 

 de Gregorio [No. i, p. 248] has recently proposed to make into a new subgenus, I)emi- 

 clausa ; this, however, is against all rules, as L. radiata is clearly the type species of 

 the genus. If, therefore, the separation is to be made, it is the other group that must 

 be renamed and removed. Lemiclausa is an absolute synonym of Ltmulif.es. 



This species was figured by Lonsdale as Lunulites urceolata, Lamk., but from the 

 latter it widely differs in the fact that the vibracularia are connected by depressions 

 into long radial lines ; in L. urceolata they are disconnected. 



From Lunulites radiata, Lamk., this differs by the gradual transition from the vibra- 

 cularia to the normal zocEcia, and by the presence of a lamina and tubercles on the rim 

 of the opesia. The species agrees most closely with L. suhplana, Eeuss [No. 3, p. 264, 

 pi. xi. fig. 108], but the apertures in that species are not clithridiate, nor does there 

 seem to be a gradual transition from vibracularia to zooecia. It clearly differs from 

 Lunulites quadrata, Reuss [Cellepore quadrata, Eeuss, No. i, p. 95, pi. xi. fig. IT; in 

 the explanation of the better figure given in Eeuss, No. 1 1, pi. xxviii. fig. 18, the species 

 is called Lepralia tetragonal, by the form of the aperture and the absence of the raised 

 rim immediately around it. The original figure gives a suggestion of a similar passage 

 from vibracularia to normal zooecia. 



In the main character of this species it resembles Lunulites goldfussi. Hag. [No. 2, 

 p. 102, pi. xii. fig. 5], but that differs by the irregular distribution of the vibracularia. 



Genus Biselenaria, nov. nom. 



Sjm. Biplotaxis, Reuss, 1867, non Kirby, 1837, Ueber Bry. <leut. Thiteroligocans, Sitz. k. Ak. Wiss. 

 Wien, Bd. Iv. Abth. i. p. 231. 



Diagnosis. A Membraniporid with a bilaminate zoarium, which is small and circular 

 and discoid in form ; typically the form is bun-shaped. The zooecia of the upper layer 

 have regular Membraniporidan apertures, with numerous normal vibracularia irregularly 

 scattered, or one to each zooecium. The zocecia of the lower surface are much modified ; 

 the aperture is contracted by the great thickening of the peristome ; in the zoojcia near 

 the centre the aperture is sometimes completely closed or persists as a long narrow slit ; 

 the vibracularia are similarly modified ; some of the peripheral zooecia more nearly 

 resemble those of the upper layer. 



Type species. Biselenaria placentula (Reuss), op. cit. 



Remarks on the Genus and its Affinities. — Eeuss practically founded his genus Diplo- 

 tixis simply on the one character of its bilaminate zoarium ; the species included in 

 it are forms of much interest, and there seems to be no reason to question the validity 



