ON THE BKITISH SPECIES OF OKISIA. 129 



A comparison of the ovicells (and especially of their aper- 

 tures) of various forms of Crisia has led me to the conclusion 

 that the British fauna includes more species of tliat genus than 

 are usually recognised. Although the constant occurrence of 

 a particular form of ovicell might possibly be explained by the 

 assumption of a definite correlation between the variations of 

 the zooecia and of the ovicells (the ovicell being regarded as a 

 modified zooecium), I do not think that this would give a suffi- 

 cient explanation of the facts. I find, indeed, that the essential 

 characters of the ovicells are extremely constant, in spite of 

 the occurrence of variations of no inconsiderable magnitude in 

 other parts of the colony. 



The following specific diagnoses, which are necessitated by 

 the results which I have arrived at, have been drawn up 

 on the model of those given by Hincks in his well-known 

 ' History of the British Marine Polyzoa,' New lists of synonyms 

 appear to nie to be also necessary, in spite of the recent appear- 

 ance of Miss Jelly's admirable catalogue,^ to which I must 

 express my great indebted uess. My lists do not profess to be 

 more than a selection of those works in which particular 

 species have been described or figured in sufficient detail to 

 make their identification fairly probable. In many cases I have 

 been obliged to give up the attempt to identify the species to 

 which the description refers, 



C. denticulata, Lamarck. Plate XII, figs. 1 — 3. 



Zoarium large, erect, of rather straggling habit ; the 

 average height of well-grown colonies about one inch ; the 

 branches well separated from one another, and with very 

 little tendency to curve inwards. In tern odes broad and 

 flattened, but usually with a slight convexity running longi- 

 tudinally along their anterior face, frequently with a double 

 curve of such a character that if the lower part of the 

 internode is convex towards the right side (e. g.) the upper 



^ E. C. Jelly, ' A Synonymic Catalogue of the Recent Marine Bryozoa,' 

 Loudon, 1889. 



