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 waters 

 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 difi'ering 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. Rosselii 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. Tubuliporidae. 

 Genus Diastopgra (Lamouroux). 

 Diastopora Sarniensis, n. sp. PI. XI. figs. 4-6. 

 JD. strato niveo, punctate, opaco, nullis lineis radiatis diaphanis 

 notato ; cellnlis longiusculis, suberectis, punctatis ; cellulis qui- 

 busdam capsula (forsitan ovicellula) umbone conspicuo mediano 

 perforate iustructa, superne ecclusis. 



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 



