Report of tse State Geologist. 



I!)7 



cididm .mikI its allies, unite t<> form an irregular mass or net-work. 

 It is to a certain degree true thai the spicules in a given species 



or genus have the same general aspect; and while they abound 





PL 



M 

 w 





Fig, MM.—Tkecidinm mediterraneum. Interior 

 of the brachial valve; showing the loose 

 spiculization of the shell-substance about the 

 brachia.— (Woodward.) 



Fig. 104.— Portion of the mantle of Tere 

 bratulina caput-serpentis, showing 

 spicules.— (Hancock.) 



in most genera, there are a few (M agellania, Terebratella, 

 Lingula) in which they are absent, or have not been observed. 

 The mantle extends to the edges of the valves and its outer 







^Mc 



Fio. 105.— Spicules of Terebratidina, greatly enlarged.— (Hancock.) 



margins are thickened, and set with stout chitinous setae, each 

 of which is lodged in a follicle or sac. The form and exterior 

 of these setae varies somewhat in different generic groups ; in 

 1891. 63 49 



