REPORT ON THE GEPHYREA. . 15 



Genus 7. Phascolion, Theel (Selenkn aud de j\Iau). 



The animals of this genus live in tubes or in shells of Molluscs. The longitudinal 

 musculatui'e is continuous and not divided up into distinct bands. The tentacles are smaJl 

 and finger-like, and are arranged in a circle round about the mouth. There is only a 

 single, fixed segmental organ. The intestine has only a few coils, or it may be none at all, 

 but there are always some large loops which are attached by the so-called fixing muscles. 

 The hooks of the proboscis often fall ofi" at an early stage. The proboscis has either one 

 or two retractor muscles. The posterior half of the body frequently with attaching papillae 

 {Haftpapillen). They are found in all seas, but especially in the colder waters. 



It seems extremely probable that the species of the genus Phascolion do not form a 

 compact, closely related group, but that they have developed independently from various 

 true Phascolosomata. One marked characteristic of the species of Phascolion is the dis- 

 appearance of one of the two segmental organs. Noteworthy also is the shortening of 

 the intestine, associated with the assumption of the looped instead of the spirally coiled 

 form. Now since all the species of Phascolion live in Mollusc tubes, the change of habitat 

 must have reacted on the anatomical structure ; it may, for instance, have to do with 

 the degeneration of one of the segmental organs, and it may be that the burden of the 

 shell has brought about the early attachment of the intestine by means of the fixing 

 muscles. The fact that in many species of Phascolosoma, which inhabit Mollusc shells or 

 tubes, one of the segmental organs is often absent but the coiled intestine apparently 

 not shortened, shows us how such a degeneration as that of the species of Phascolion has 

 arisen. In the latter, as we have mentioned, the spirally coiled intestine is unwound 

 into loose loops, and there are transitional states between the two conditions. 



If the supposition be correct that the species of the genus Phascolion are connected with 

 those of the genus Phascolosoma by diverse lines of origin, the genus Phascolion should 

 be resolvable into several, since the system ought to be the expression of phjdogenetic 

 relationship or genetic history. But since it is not possible to recognise these genetic 

 relationships, far less prove them, I therefore retain for the present the single genus 

 Phascolion. 



14. Phascolion squamatum, Koren and Danielssen (PL IV. figs. 18-19). 



Fhascolosomasquamatum, Koren and Danielssen, Fauna littoralis norvegiae, Heft iii pp. 130, 131, 



Tab. xiii. fig. 11, Tab. xiv. figs. 14, 15. 

 Phascolosoma squamatum, Selenka and de Man, Die Sipunculiden, &c. (loc. cit.), p. 40. 



The body is four times as long as it is broad. The proboscis is two and a half timas 

 as long as the body. The skin is studded all over with large, flat, more or less protrusive 

 scales. On the proboscis are fine papillae, arranged in separate rows and at a distance 

 from one another, but somewhat more closely set near the tentacles. The tentacles are 



