1724 THE VOYAGE OF H.M.S. CHALLENGER. 



horn. Aboral hinge with two pyramidal, horizontal, caudal horns of different sizes, the dorsal 

 smaller than the ventral. Lateral margin of each valve on one side with twelve to fourteen strong 

 conical teeth (fig. 12). Lips of the narrow mouth thickened (fig. 11). 



Dimensions. Length of the shell 0'3, height 0'27, breadth 0'21. 



Habitat. Tropical Atlantic, Station 342, depth 1445 fathoms. 



2. Conchonia triodon, n. sp. (PI. 124, figs. 13, 14). 



Shell laterally compressed, with two very unequal valves. Dorsal valve (fig. 14) larger, hat- 

 shaped, on the apex with a large pyramidal horn which is half as long as the shell, curved and 

 directed backwards. Ventral valve (fig. 13) smaller, boat-shaped, without apical horn. Aboral 

 hinge with two pyramidal caudal horns of different sizes, the dorsal horn twice as long as the 

 ventral. Lateral margin of each valve on one side with twelve to fifteen conical teeth. Perhaps 

 the larger horned valve (fig. 14) may be the ventral, and the opposite smaller hornless (seen from 

 above in fig. 13) the dorsal valve. 



Dimensions. Length of the shell 0'21, height 017, breadth 012. 



Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



3. Conchonia tetrodon, n. sp. 



Conchura tetrodon, Haeckel, 1882, Manuscript. 



Shell subspherical, with two nearly equal hemispherical valves, which are very thin-walled and 

 similar in structure to those of the Coelodendrida, with very irregular roundish pores of different 

 shapes and sizes (compare PI. 121, fig. 3). Lateral margins of the valves with very numerous and 

 irregular, thin, bristle-shaped teeth, similar to those of some Coslographida (compare PI. 127, fig. 8). 

 Aboral hinge with two equal, conical, caudal horns, which are straight, parallel, and half as long as 

 the shell. Two similar straight conical horns are opposed on the poles of the sagittal axis, and arise 

 from the apex of the two valves. This remarkable species may perhaps better represent a separate 

 genus, Conchura, forming a direct transition to the ancestral form of the Coelodendrida, Ccelodoras ; 

 it differs from the latter in the absence of a galea or hollow conical cupola on the apex of each 

 valve, and in the solid, not hollow structure of the horns. 



Dimensions. Diameter of the shell 0'24, length of the two sagittal horns 01, of the two caudal 

 horns 012. 



Habitat. Indian Ocean, Cocos Islands (Eabbe), surface. 



Genus 725. Conchopsis, 1 Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 6. 



Definition. C oncharida with dentate lateral margins and a sharp sagittal 

 keel of the compressed valves, without horns on the hinge. 



1 Conchopsis = Similar to a bivalved shell-fish or mussel ; 



