Oeneral History of the Marine Polyzoa. 475 



its specific distinctness, and placed it in the genus Micro- 

 pora *. It may be well to note some of the principal differ- 

 ences between the two forms : — i. There are important 

 differences in the orifice ; that of M. perforata is very inferior 

 in size, arched above and perfectly straight below, and very 

 narrow between tlie upper and lower margins ; it is also much 

 raised above the front wall. That of M. lepida is more than 

 twice as large ; the angles at the junction of the sides with 

 the inferior margin, so marked in the other form, have disap- 

 peared, and the orifice is almost subelliptical. 



ii. In MacGillivray's species the cell tapers off abruptly to 

 the top, which is much narrower and more pointed than in 

 M. lepida, and the raised margin is only carried to the base of 

 the orifice^ which stands out prominently at the apex of the 

 cell, whilst in M. lepida it is carried to the top of the orifice 

 and encloses it. Indeed there is a striking contrast between 

 the zooecia of the two species in size, form, and general 

 character. 



iii. In M. perforata the avicularia are small and placed at 

 the top of the cells immediately above the orifice on a slight 

 elevation, and are furnished with a triangular mandible. In 

 M. lepida they are scattered amongst the zooecia and occupy 

 a distinct area of considerable size ; they are comparatively 

 large ; the beak is broad below, where there are two strong 

 denticular processes on which the mandible works, and tapers 

 upward, curving slightly to one side ; the mandible I have 

 not seen, but there can be little doubt that it is elongate, 

 tapering, and pointed. 



iv. It may be added that in M. perforata there is a stout 

 spine on the side of the orifice above, which is wanting in 

 M. lepida^ and that the ovicells, judging from MacGillivray's 

 figure, differ in shape. That of the last-named species is 

 small and globose. 



Not only are these forms undoubtedly distinct specifically, 

 but I am by no means satisfied that they belong to the same 

 genus. Mertihranipora perforata, MacG., is a characteristic 

 Micropora ; but Monojiorella lepida has several features which 

 serve to indicate its affinity with the Microporellidge. The 

 termination of the cell-margin at the base of the orifice, 

 leaving it free and truly " apical " fj is, so far as I know, a 



* " Bryozoa from Bairusdale," Quart. Journ. Geol. Soc, Nov. 1882. 

 Referring to the two forms lie says, " I think they must not only be 

 united generically, but can only rank as specific varieties." See also 

 *' Tertiary Chilostomatous Bryozoa from New Zealand," Quart. Journ. 

 Geol. Soc, Feb. 1887. 



t See Busk's diagnosis of the genus Micropora, * Challenger ' Report, 

 p. 70. 



