472 M. K. A. Zittel on Fossil Lithistidm. 



sole distinction is the presence in Siphonia of a depressed cen- 

 tral cavity, into which the ostia of the curved main canals 

 open ; but when the central cavity is broad and shallow, the 

 canals also become more upright, and forms are produced 

 which immediately approach Jerea. The structure of the 

 skeleton is the same in the two genera. 



This relationship of the two genera is reflected in the lite- 

 rature of the subject. Parkinson's diagnosis of Siphonia 

 applies equally well to both ; and among his species are two 

 Jerece. Of the three original species of Mantell's Choanites, 

 two belong to the Hexactinellid* ; the third (0. Konigi) is a 

 Siphonia. In ' Medals of Creation ' (2nd ed. pp. 230, 233) , 

 Mantell separates Choanites and Siphonia, distinguishing the 

 former by the absence of a stalk furnished Avith tubes. By 

 most subsequent authors Choanites is dropped and united with 

 Siphonia. Cunnington, indeed (Institut, 1849, xvii. p. 14), 

 finds generic distinctions in the deep central cavity and a 

 supposed spiral canal ; but no such canal is to be seen in the 

 figures of Mantell and Dixon, or in specimens from England. 

 Goldfuss, F. A. E,omer, Reuss, D'Orbigny, &c. combine 

 very different sponges under Siphonia ; Courtiller refers to it 

 a great many true Jereoi j while Fromentel and Pomel place 

 the two genera in different families, and divide each of them 

 into several genera. Parkinson's name is retained for these 

 sponges, because it has been almost without exception em- 

 ployed for the typical species (e. g. Siphonia piriformis, 

 tulipa, jicus, nuciformis, &c) ; and these species would cer- 

 tainly have been included by Parkinson under Siphonia. 

 The genus is confined to the Cretaceous formation. The 

 lobate forms may constitute a special subgenus {Hallirhoa, 

 Lamx.). 



A. Of typical Siphonice may be mentioned : — 



1. Siphonia piriformis, Goldf. vi. la; Mich. Ic. xxxiii. 1. 

 Senonian. 



2. Siphonia tulipa, Zitt. ■^. Cenomanian, Blackdown. 

 Siphonia piriformis, Sow. Geol. Trans, ser. 2, vol. vi. pi. xv. a. 

 Siphonia Wehsteri, Queust. (non Sow.), Petr. cxxxv. 15-19. 



* This species, which is very abundant in the Greensand of Blackdown 

 and Halden, has received a new name. It is generally united with 

 Siphonia piriformis, Goldf., but is distinguished by the sudden constric- 

 tion of the pyriform head immediately above the very long slender stalk, 

 by the coarse curved aud radial canals, and by the microstructure of 

 both the head and the stalk. Quenstedt has separated it from S. piri- 

 formis, but identified it, erroneously, with Jerea Wehsteri, Sow., of which 

 Sollas has lately given a good desciiption and figures. Siphonia Fittoni, 

 Mich., is more nearly allied to "S". piriformis, Goldf., than to S. tulipa. 



