7 8 CCELENTERATA. 



little chitinous cups or " cellules," each of which must have 

 contained a polypite, and which agree with the similar struc- 

 tures of the Graptolites in partially overlapping one another ; 

 thus differing from the " hydrothecae " of the Sertularians. 



In Dictyonema (fig. 26) we have organisms resembling 

 Dendrograpsus in many respects, but not possessing any foot- 



Fig. 26. Dictyonema retiforme, Hall. (After Hall.) 



stalk. The frond is branched and plant-like, and is fan-shaped 

 or funnel-shaped in form. It is not certainly known whether 

 the organism was attached by its base or not ; but there is the 

 strongest probability in favour of its having been fixed. The 

 branches radiate from the base, running nearly parallel with 

 one another, and often bifurcating. They are united to one 

 another at short intervals by numerous, irregular, slender, 

 transverse processes or dissepiments, and they bear small 

 ''' horny cups or " cellules " like those of the Graptolites. Dic- 

 tyonema ranges from the Upper Cambrian to the Middle 

 Devonian. The genus bears a close superficial resemblance 

 to the Fenestellce or Lace-corals (belonging to the Poly zoo) ; 

 but the latter have a calcareous skeleton, and have no " cel- 

 lules." Besides the above-mentioned genera, Calfograpsus 

 and Ptilograpsus may with great probability be referred to the 

 Sertularida; as may, perhaps, be the obscure fossils Butho- 

 grapsus and Thamnograpsus. All these genera are Silurian or 

 Upper Cambrian in age. 



