238 
THE VOYAGE OF H.M.S. CHALLENGER. 
whicli are prolonged from tlie outer surface of the test in the ease of most Molgulidse and 
some Cynthiidae amongst the Simple Ascidians, and in Polyclinum sahulosum, Giard, 
a member of the present family. In the description of the last named form, Giard ^ 
makes no mention of imbedded sand grains in the test, and consequently we may infer 
that the sand is merely adhering to the surface of the haii-like processes which he describes. 
I think it is probable that von Drasche’s Aplidium asperum belongs to the present genus. 
He does not figure a section of the test, but from his description ^ it appears that there 
are many imbedded sand grains. It differs from all the Challenger species. 
One result of the presence of imbedded sand in this genus is that the colony is 
rendered hard, brittle, and opaque. Tlie Aseidiozooids are generally not visible 
externally, and are in some cases rather difficult to dissect out both on account of their 
small size and because of the surrounding sand grains. 
The condition of the stomach varies in the genus; in some eases it is smooth {Psamma- 
plidium s-pongiforme), in others it is folded longitudinally {Psammaplidium incrustans). 
In external form also the species vary greatly, as is shown in the following synoptic 
table of the genus.^ 
Psammaplidium. 
Colony thin and 
incrusting. 
I 
P. effrenatum. 
Colony massive. 
External part 
of test modified 
to form a 
distinct layer. 
P.flavum. Colony ovate. 
Colony broken up into 
narrow lobes. 
External layer 
of test not 
modified. 
P. reUforme. 
Colony irregularly 
lobed. 
Much imbedded 
sand. Colony 
quite stiff. 
I 
P. suhviride. 
Not much 
imbedded sand. 
Colony firm 
but not stiff. 
Colony consisting 
of short cylindrical 
lobes arising from 
a common base. 
Lobes of the 
colony quite 
irregular. 
Stigmata not 
P. ovatum. Stigmata very narrow, very narrow. 
P. exiguum. 
Stomach 
globular, 
smooth 
walled. 
Stomach 
quadrate, 
folded 
longitudinally. 
P. spmgiforme. 
P. rude. 
^ Recherches sur les Asc. Comp, ou Synascidies, Archives d. Zool. exfir., t. i. p. 643. 
2 Die Synascidien der Bucht von Rovigno, p. 26. 
To these eight species must be added a ninth, Pscmrria/plidium pyriformis (see Appendix B. at the end of this 
Rejx)rt). It is closely allied to Psammaplidivm suhviride, but differs from that species in its pyriform shape, its colour, 
and the condition of its mantle and branchial sac. 
