REPORT ON THE RADIOLARIA. 1723 



7. Conchidium magasella, n. sp. 



Shell laterally compressed, with two equal valves, very similar to the preceding species, but 

 differing in the following characters : Proportion of the three axes =6:4:3. Margins of the 

 valves with smaller and more numerous teeth ; on each side of one valve sixteen to eighteen short 

 conical teeth. Pores smaller and more numerous, about as broad as the bars. 



Dimensions. Length of the shell 0'24, height 0'16, breadth 0'12. 



Habitat. Indian Ocean, Madagascar (Rabbe), surface. 



8. Conchidium productum, n. sp. 



Shell laterally compressed, prolonged, with two equal valves, similar to the two preceding 

 species, differing in the following characters : Proportion of the three axes = 3:2:1. Margins of 

 the valves smooth in the anterior and posterior quarter, dentate in the middle lateral half ; on each 

 side of one valve ten to twelve strong conical teeth. Horns of the aboral hinge prolonged, conical, 

 half as long as the shell, the ventral somewhat larger than the dorsal. Pores regular, circular, twice 

 as broad as the bars. 



Dimensions. Length of the shell 0'25, height 015, breadth 0'08. 



Habitat. North Atlantic, Station 354, surface. 



Genus 724. Conchonia, 1 n. gen. 



Definition. C oncharida with the lateral margins of the valves dentate, without 

 sagittal keel, but with an apical horn on the poles of the sagittal axis, and with two 

 caudal horns on the hinge (a dorsal and a ventral). 



The genus Conchonia is closely allied to the preceding Conchidium, its ancestral 

 form, but differs from this and from all other Concharida in the development of horns 

 on the poles of the sagittal axis. These are probably of great morphological importance, 

 since they represent the beginnings of the hollow tubes arising from the poles of the 

 sagittal axis in all Coslodendrida and Ccelographida. In one of the three observed 

 species each valve possessed an apical or sagittal horn, whilst in the two other species 

 one valve only was provided with a horn. Since I observed one specimen only of each 

 species, I cannot say whether this difference is important and of constant generic value. 



1. Conchonia diodon, n. sp. (PI. 124, figs. 10-12). 



Shell laterally compressed, with two very unequal valves. Dorsal valve smaller, hat-shaped, on 

 the apex with a fenestrated protuberance which is similar to the galea of the Coelodendrida, and 

 bears a short, conical, backwardly-directed horn. Ventral valve larger, boat-shaped, without apical 



1 (7<mc/wmz=Bivalved shell like a mussel ; xoyxx, ox. 



