ORDER II 



CALCISPONGIAE s Y< < N KS 





layer; oscula invent here. lut absent on other parts d 

 composed i.f very coarse, anastomosing til.r.-. < Jretaceous. 



(loldf. -p. 



exterior. sk.-i.-t..n 

 /'. ////'//<//'/,/////',//,, 



Order 2. SYCONES. Haeckel. 



//",///.< /,">-,,<,,/ l,if .<iin/'/''- tnnl.< 

 f'1 if. 



reference to the 



wUm 



Mostly small, delicate forms inhabiting shallow water. 



/'/*/".<////, Zitt., from the I'pper .Inra.-siY of Streitbrrg. is a small, eylin- 

 drii-al, or eonical form agreeing with living Sycons in the arrangement of its 

 radial canals. 



To the Sycons, also, Rauff assigns the calcareous sponge ^ihim-tozoa described 

 by Steinmann (.lahrb. 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 i'n*'itriti. 



The oldest Sycons are Sollasia, 

 jjtfliblysiphonellct, and Sebargasia, 

 Steinm., from the Carboniferous 

 Limestone of Asturias. In the 

 Triassic of St. ('assian and See- 

 landalp, near Schluderbach in 

 Tyrol, are found Colospongia, 

 Thaumastocoelia, and Cryp- 



';,, < t ,.;,,, Tlmltnm nnrit ]: "' '"'-'" " >tiH" "*, Mant. sp. Aptian ; Farrin-don, Berk- 



M, Steinmann. l/iaUtmopOia, 8li . re> A ^ 15l ,sh-lik ( - colony, one person sliced open; natural 

 Roem., and Barroisia, Steinm., size. ^ Mvido^cut l^ro^otMquely, ^, o, Janction Of 



i -r- i n two se-inents; '., Cloaca; o, Osculuni ; (/. Hadial canals. < . I'. 

 occur 111 the Lower and Middle Three-rayed skeletal spi.-ul.-s. " l and r-' (1 (after Steiniuann). 



Cretaceous. 



l',<tm>i*i<i (FentricutiUs, Zitt. non Defr., SpJuurocoelia, 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 tubitorm. 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. B. helvetica, Lor. 

 sp. Aptian : La I're>ta, Swit/erland. 



Range and Distribution of Fossil Sponges. 



The phylogeny of the J///."/syo/,r/iae, Ccratospongiae, and a part of the 



', 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 F 



