British Hydrozoa, Actinozoa, and Polyzoa. 89 
granular membrane. The oral aperture occupies nearly or quite 
half the cells, and has a somewhat three-lobed outline, from the 
fact that midway up each side there is a slight constriction of 
the orifice. The peristome is totally devoid of spines, and is an 
elevated crenated rim which is continuous with, and indeed re- 
presents, the cell-margin. The avicularia are very sparingly de- 
veloped. When present, they are situated between the cells, are 
acutely triangular, and have the much-produced mandible di- 
rected upwards. The ovicells are semielliptical, tumid, and 
smooth, but having on the front a triangular space which is 
minutely granular. The colour of the species seems to be in- 
variably pale olivaceous green. 
Membranipora sacculata is not uncommon in the deep oetere 
of the Shetland Sea, ranging from seventy to one hundred fa- 
thoms or more, and encrusting both stones and shells. 
It is allied both to M. cornigera and M. Rosselii. The mem- 
brane which closes the cells is thinner than in either of those 
species. In the form of its cells it approaches very closely to 
the former, but never shows a vestige of spines, still less of the 
curious branched processes, and has avicularia differing totally in 
character from the numerous elliptical blunt-mandibled organs 
of that species. It may be known from M. Rosselii by the form 
of its cells, which are regularly rhomboidal and broader in pro- 
portion to their length. In M. Rosselit the polyzoary has the 
appearance of being formed of a number of loops, caused by the 
peculiar elongated ovate form of the cells, which are wider above 
than below, and by the fact that the raised marginal rim is more 
strongly developed round the summit of the cells than at the 
sides, whereas in M. sacculata the rim is of equal thickness 
throughout. In typical specimens of the former, moreover, the 
orifice occupies a much smaller proportion of the whole cell than 
is the case in the latter species. 
Fam. Tubuliporide. 
Genus Drasrorora (Lamouroux). 
Diastopora Sarniensis, n. sp.. Pl. XI. figs. 4-6. 
D. strato niveo, punctato, opaco, nullis lineis radiatis diaphanis 
notato; cellulis longiusculis, suberectis, punctatis; cellulis qui- 
busdam capsula (forsitan ovicellula) umbone conspicuo mediano 
perforato instructa, superne occlusis. 
Diastopora Sarniensis consists of a milk-white, opake, punc- 
tured crust spreading upon shells, with a round or lobulated 
outline, and sometimes reaches three-quarters of an inch in 
diameter. The polyzoary is not marked with the alternate 
opake and transparent radiating lines of D. obelia, and its 
