84 SIDNEY F. HARMER. 



has described it in Idmonea atlantica (p. 443), in I. ser- 

 pens [= T. liliacea of the present paper] (p. 446), in T. 

 fimbria [= T. aperta] (p. 455), in T. flabellaris (pp. 

 456, 457), and in T. lobulata (p. 457). The descriptions 

 there given are not, however, sufficiently precise to be used in 

 discriminating the species, nor are they illustrated by figures 

 which really show their character. Waters (44, pp. 256 — 259, 

 and 43, p. 339) has described the oceciostome in one or two 

 species of Tubulipora or Idmonea; and Kirkpatrick (22, p. 

 22, pi. iv, figs. 6 a, 6 b) has described and figured the ocecio- 

 stome of I. pulcherrima. These are almost the only refer- 

 ences I have been able to find to the oceciostome of recent 

 species of Tubulipora. It appears to me that a Tubuli- 

 pora colony reaches its fully adult condition when the ovicell, 

 with its oceciostome, is fully formed. If this view be correct, 

 the importance of the oceciostome as a specific character is 

 intelligible. Colonies in which this structure is not yet deve- 

 loped are in a state of immaturity. It is perhaps as reason- 

 able to characterise a species of Tubulipora without taking 

 account of its oceciostome as it would be to describe a new 

 species of Cervus without describing the form of the antlers. 

 It is unfortunately impossible to describe the oceciostome of a 

 Cyclostome in the majority of cases, and particularly in fossil 

 specimens; but I think the description of this structure should 

 be an essential part of a diagnosis wherever it can be given. 



The absence of the oceciostome in a given case may depend 

 on the season of the year at which the specimen was obtained. 

 It is, for instance, somewhat difl&cult to find the ooeciostomes 

 of the British species in colonies collected in the spring, in 

 which the formation of the ovicell is beginning ; but it is easy 

 to find them in uninjured healthy colonies collected in the 

 summer. 



The following table illustrates the use which can be made 

 of the oceciostome in distinguishing the species treated of in 

 this paper. The " lower " surface of the colony is that by 

 which it is fixed, so that '' upwards " means away from the 

 basal surface : 



