474 M. K. A. Zittel on Fossil Lithistidce. 



the outer surface. Surface with numerous, unequal, scattered 

 small ostia, from which canals ran to the centre of the sponge. 

 These ostia gradually disappear on the stalk. 



Skeleton composed of four-armed corpuscles of considerable 

 size ; the arms usually smooth near the point of union, but 

 sometimes with blunt processes ; their ends more or less 

 branched, sometimes even enlarged into interlocked balls. In . 

 some species the arms, or some of them, divide into two main 

 branches. Isolated forked ancliors and simple bacillar spicules 

 occur. 



The genus was well characterized bj Lamouroux in 1821. 

 Goldfuss describes several species under the names of Jerea^ 

 Siphonia, and Manon ; and Michelin also mixes Siplionia and 

 Jerea ; but D'Orbigny ratlier limits Lamouroux's conception, 

 and separates the forms with a dihited root under the name 

 oi Rhysospongia. Such roots had previx3usly been referred by 

 Michelin to Folypotliecia. Fromentel separated the com- 

 pound forms as Polyjerea ; and Courtiller and Pomel divide 

 Jerea into several genera. The former retains the naiue only 

 for those with a truncate vertex ; those with a depression form 

 the genus Cujmh'na. Many true Jereoe, are also referred by 

 him to Siphonia., and those with a large root to Rhysospongia 

 D'Orb. As the supposed epitheca of BMzospongia lias no 

 existence, that genus is superfluous, as also RMzosteh^ Rhizo- 

 gonium, and Rizogonima^ Pom. Pomel divides the compound 

 Jerecc into several genera ; Polyjerea is retained for the forms 

 with basal prolification, such as J. ccesintosa and gregaria^ 

 Mich., 8. ternata, Peuss, &c. ; Callojerea and Dichojerea are 

 proposed for the branched forms, and, being founded solely 

 upon external characters, include very heterogeneous elements. 



The genus Jerea first appears in the Cretaceous, and possibly 

 extends into the Miocene, if some of Pomel's species really 

 belong to it. As typical species may be cited : — 



*1. Jerea pyriformis^ Lamx. Exp. p. 79, Ixxviii. 3. Ceno- 

 manian. 



Jerea pyriformis and elomjata p. p., Micli. Ic. xxxvi. 3, and xxxix. 4. 

 Jerea amygdaloidea, Giimb. Ostb. Grenzgeb. p. 771. 



2. AlcyonoUthes stadensis, Blum. Spec. Arch. Tell. ii. 

 figs. 5, 6. 



Siphonia cucumis, Menke, Jahrb. 1841, ii. fig. c. 



Siphonia Kraiissi, Hag. 



Jerea pyriformis and elongata p. p., Mich. I. c. 



Jerea pyriformis and ijttricata, Court. Ep. xxxiv. 2, 3. 



3. Jerea Quenstedti, Zitt., Q^iadrahis-chdW., Linden, near 

 Hanover. 



Siphonia ficusy Quenst. Petr. cxxxv. 20-23. 



