428 



GEPHYREA 



water became stagnant and impure the anterior end with ex- 

 panded branchiae was often protruded somewhat above the surface 

 of the sand." 



The genus Phascolosoma contains at least twenty-five species, 

 for the most part small. Ph. margaritaceum, however, measures l 

 10 cm. in length, and Ph. flagriferurn, 13 cm. The latter is 

 produced at the hinder end of its trunk into a long whip-like 

 process, which recalls the horny spike of Goljingia. Most species 

 live free, but a few inhabit the shells of dead Gasteropods or of 



Fig. 216. Specimens of the Coral Heteropsammia cochlea, with Aspidosiphon heteropsam- 

 miarum or A. michelini living in a state of commensalism with them. (From Bonvier.) 



Bentalutm, or the abandoned tubes of worms. They occur in 

 practically all seas. 



Bendrostoma contains but five species, which are all found 

 within the tropics in the Pacific or in the West Atlantic. They 

 are shallow-water forms, and some are found between tide-marks. 



Phascolion is a smaller genus, containing but ten species, which 

 may have been derived independently from different species of 

 Phascolosoma, and in this case the genus should be broken up. 

 The members of this genus live in Mollusc shells, such as 

 Dentalium, Turritella, Buccinum, Chenopvs (Aporrhais), Xassa, 

 Strombus, and generally acquire the coiled shape of their host. 

 They are usually attached to the shell by means of certain 

 1 Selenka, Challenger Reports, vol. xiii. 1885. 





