460 PHORONIS 



adult as marking the anterior end of the animal, the anus the 

 posterior. The short line between the mouth and anus across 

 the centre of the tentacular crown marks the dorsal surface ; and 

 the line running all round the trunk from anus to mouth, the 

 ventral. In fact, in its usual position in its tube Phoronis is 

 lying on its ventral surface, its back faces upwards, and the 

 anterior and posterior ends lie on one side or the other. 



Species and Affinities.- In his exhaustive memoir on the 

 anatomy and histology of Phoronis, Cori enumerates seven 

 different species, and quotes the characters of each as enumerated 

 by eight different authors. He, however, reserves his opinion 

 as to the identity or distinctness of some of these species. 

 Benham in his account of Ph. australis enumerates five species, 

 including amongst them Ph. ovalis, which, however, he regards 

 as probably a young form, an opinion in which Cori coincides. 

 The latter regards it as possibly a young form of Ph. hippocrepia. 



Without comparing specimens of each of the alleged species, 

 it is difficult to come to any very satisfactory solution of the 

 problem of how many distinct species are at present known, but 

 it seems probable that there are at least six. 



(i.) Phoronis hippocrepia Wright. Under this name is included the first 

 form, described and named by Wright in 1856 ; also Ph. ovalis, described two 

 years later by the same observer as a distinct form, though it now seems 

 probable that it is but a young form of Ph. hippocrepia. The Crepina yracilis 

 of van Beneden is probably identical with this species. 



This species occurs in membranous tubes embedded in limestone, corals, 

 or oyster shells. Its length varies from 1'5 to 15 mm. The number of 

 tentacles varies from 16 to 86. It has been found off the coast of Devon- 

 shire and in the Firth of Forth. 



(ii.) Phoronis Icowalevskii Caldwell. This name is given by Benham to the 

 species from Naples described by Caldwell, and replaces the name Ph. 

 caespitosa, which was given, but subsequently withdrawn, by Cori. This 

 species is found in the Bay of Naples, living in considerable colonies on sub- 

 marine piles and posts. It is not firmly attached to its substratum. The 

 tube may be coated with sand or other foreign particles. The length of the 

 individuals varies from 3 to 39 mm. The lophophore is simple, with from 

 50 to 100 tentacles. 



(iii.) Phoronis australis Haswell. This is the giant of the genus, the length 

 of the individuals being from 3 to 5 (76-127 mm.) or rarely 6 inches. It 

 lives in delicate transparent tubes, interlacing the walls of the tube of a 

 sea-anemone, Cerianthus. The arms of the lophophore coil into two spirals. 

 The colour is reddish or purple. Found in Port Jackson. 



(iv.) Phoronis buskii M'Intosh. This species was dredged by the Challenger 



