83 
McLean . — On the Fossil Genus Sporocarpon. 
a wide meshwork, as viewed in tangential section, the interspaces being 
filled in with slighter tubules. The larger tubes in this type bear the 
external orifices at the nodes of their mesh. These two forms are not, 
however, sufficiently distinguished by this peculiarity alone to warrant their 
specific segregation from one another. All the tubes are quite thin walled, 
and there is no appearance of contents, or of finer lateral openings, or 
appendages such as might be suggested by the analogy of the investment 
of tangential tubules in Traquairia . Openings to the interior exist, and the 
capsular contents of sporoids and small spores are quite normal, except 
that the capsule wall may show a very delicate reticulation (slide 1503, 
Williamson), an appearance also noted in Traquairia Carruthersii (W . Coll. 
1066, 1074, 1077). The capsule sometimes shows a double wall, but this is 
met with occasionally in all species and may be the universal condition. 
On the other hand, the external surface is peculiarly interesting. It often 
appears to be covered with a dark membrane, double in places, through 
which the exoscopic apertures thrust themselves, while many specimens 
have small thin-walled vesicles like bubbles, borne attached organically to 
the outside of the tubular envelope. 
Putting these aside for the moment, let it be noted that the species is 
not only highly gregarious, but actually colonial, several individuals being 
massed together in one confluent envelopment of tubes. This marks 
a distinct departure from the usual Traquairidean type and bespeaks an 
approach to the Pharetrone sponges. Many cases of confluent individuals 
show one or more of the attached individuals collapsed, and when this is 
the case the collapsed one always has a very exiguous envelope of tubes, 
with a dark and well-marked sphere wall. Now I would suggest that 
these are the younger members of the colony, as yet unstrengthened by the 
full development of their envelope, and that they are formed on the outside 
of older members by the growth of the round vesicles previously spoken of, 
building up a sort of Globigerina . Thus the colony would be regarded as 
formed by superficial budding, each new sphere forming from an enlarge- 
ment of one of the peripheral tubes in the older organism ; which is in 
a manner a parallel phenomenon to the secondary enlargement of the cells 
in § Eu- sporocarpon . 
One very peculiar specimen (U.C.L. Collection), mentioned in my last 
paper, shows three confluent individuals, in one of which there is an internal 
ring of wide oblong cells arranged radially, with very dark contents. These 
are very puzzling and suggest further uncomprehended possibilities in regard 
to the group as a whole (PI. X, Fig. 19). 
The lumen of each cell is confluent outwardly with a tube of the 
envelope, so that they are part and parcel of the investment system and 
not .special reproductive cells of any sort. 
Taking into consideration the colonial habit, I would hazard the view 
H 2 
