ORDER II CALCISPONGIAE—SYCONES 65 
layer ; oscula present here, but absent on other parts of exterior. Skeleton 
composed of very coarse, anastomosing fibres. Cretaceous. P. infundibuliformis, 
Goldf. sp. 
Order 2. SYCONHES. Haeckel. 
Walls traversed by simple canals disposed radially with reference to the cloaca 
and opening into it. Skeletal elements very regularly arranged. 
Mostly small, delicate forms inhabiting shallow water. 
Protosycon, Zitt., from the Upper Jurassic of Streitberg, is a small, cylin- 
drical, or conical form agreeing with living Sycons in the arrangement of its 
radial canals. 
To the Sycons, also, Rauff assigns the calcareous sponge Sphinctozoa described 
by Steinmann (Jahrb. f. Mineralog. 1882, II. p. 139), which is distinguished 
from all other Calcisponges by 
having a most remarkable seg- 
mentation, such as occurs in the 
Lithistid genus Casearia. 
The oldest Sycons are Sollasia, 
Amblysiphonella, and Sebargasia, 
Steinm., from the Carboniferous : pent 
Limestone of Asturias. In the * y ene 
Triassic of St. Cassian and See- E we 
landalp, near Schluderbach in 
Tyrol, are found Colospongia, 
Laube, Thaunuastocoelia, and Cryp- 
tocoelia, Steinmann. Thalamopora, ,,2erreganentonens, Mant sp. Aption; Farringdon, Bers 
Roem., and Barroisia, Steinm., size. B, Individual cut through obliquely, 5/2; a, Junction of 
: two segments ; }, Cloaca; 0, Osculum ; d, Radial canals. C, D, 
occur in the Lower and Middle hree-rayed skeletal spicules, °/; and 72/ (after Steinmann). 
Cretaceous. 
Barvoisia (Ventriculites, Zitt. non Defr., Sphaerocoelia, Steinm.), (Fig. 97). 
Occurs sometimes as simple, cylindrical, or clavate individuals, and again in 
the form of bushy stocks. Outer surface frequently constricted, summit 
arched, with osculum in the centre, cloaca tubiform. The cylindrical indi- 
viduals are composed of thin-walled, hemispherical, or compressed segments, 
which are so arranged that the roof of one segment serves also as the floor of 
the next following. The wall is everywhere perforated by simple radial canals, 
and is made up of fibres composed of three-rayed spicules. . helvetica, Lor. 
sp. Aptian; La Presta, Switzerland. 

Fic. 97. 
Range and Distribution of Fossil Sponges. 
The phylogeny of the Myzxospongiae, Ceratospongiae, and a part of the Silici- 
spongiae, owing to their perishable organisation, must ever remain involved in 
doubt. Nevertheless, isolated spicules prove the existence of Monactinellids 
and Tetractinellids in Palaeozoic seas; while in the Trias, Jurassic, and Cre- 
taceous these forms become important rock-builders, and certainly play an 
active part in the formation of hornstone, chalcedony, and flint. In the Ter- 
tiary, spicules referable to existing genera are quite common. 
VOL, I r 
