Nodules of the Trimmingham Chalk. 387 



mentioned that of fig. 3, merely, however, as an indication 

 that such spicules are not absent from the deposit, and by 

 no means as implying a belief that this particular one actually 

 formed a part of the skeleton of Discoder mites cretaceus. 



Rhagadinia Zitteli. (PI. XIX. fig. 8.) 

 Compare Zittel, Cceloptychium, Taf. vii. figs. 25, 26, 27, 30. 



This spicule is selected for representation as the largest and 

 most regular of a large number of similar forms. Its conical 

 stalk is expanded above into three broad flattened branching 

 arms, which lie in the same plane and form together a much 

 divided disk. It closely resembles the dermal spicule of 

 Rhagadinia rimosa, Roem., from which it is distinguished by 

 the simple edges of its arms, which have not the secondary or 

 minor lobations of R. rimosa, and consequently do not present 

 the same ragged appearance. In this respect it much more 

 resembles the dermal spicule of Rhacodiscula, Zitt. 



Fig. 10 may possibly be the skeletal corpuscle of this 

 species, and fig. 15 the small acerate corresponding to that 

 figured by Zittel from R. rimosa. 



Eurydiscites irregularis. (PI. XIX. fig. 14.) 



This is one of a number of similar dermal spicules, distin- 

 guished by their large size and the coalescence of the arms 

 into an irregularly lobate disk, generally less lobate than in 

 the example here figured, which is an exceptionally regular 

 form. They remind one, but for the presence of a stalk, of 

 the disks o*" Plinthosella represented in Zittel's monograph. 



These disks alone are not sufficient to characterize a genus; 

 but they must have a name, and so we designate them provi- 

 sionally Eurydiscites irregularis. Probably they will speedily 

 be identified with the outer coating of some already described 

 fossil genus ; and then the necessity for our name will cease. 

 If the genus should be related to Plinthosella, we might regard 

 fig. 17 as representing a part of one of its skeletal corpuscles. 



Nanodiscites parvus. (PI. XIX. fig. 13.) 



This is a dermal spicule, somewhat resembling that of 

 Theonella Pratti, Bow. Its simple, asymmetrical, short 

 branches give it a curious stunted appearance, which suggests 

 the name Nanodiscites, from vavo9, a dwarf. 



Compsapsis cretacea. (PI. XIX. figs. 21 and 22.) 



These skeletal corpuscles appear to approach more closely 

 those of Kaliapsis cidaris, Bow., than any other form. 



