REPORT ON THE RADIOLARIA. J 721 



Genus 723. Co7ichidium,^ Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 6. 



Definition. — C o n c h a r i d a with the lateral margins of the valves dentate, without 

 sagittal keel and apical horns, but with two caudal horns on the hinge (a dorsal and 

 a ventral). 



The genus Conchidium is the most common form of aU Concharida, and some of 

 its species occur in great numbers in the tropical zone of the Pacific and the Atlantic, 

 on the surface as well as at various depths. It differs from the preceding Conchellium, 

 its ancestral form, in the development of two caudal horns, or two strong pyramidal 

 spines which arise from the posterior end of the valves ; the dorsal horn usually is 

 smaller than the ventral. 



1. Conchidium terebratula, n. sp. (PI. 124 figs. 1, 2). 



Shell subspherical, smooth ; both valves of nearly equal size and form, hemispherical. The 

 three dimensive axes of the body are almost equal. Margins of the valves dentate in nearly the 

 whole periphery ; on each side of one valve eleven or twelve strong conical teeth, all of the same 

 size. Aboral hinge with two short and stout four-sided pyramidal horns of equal length. Mouth 

 with two equal short Ups. Pores of the shell subregular, circidar, three to four tunes as broad as 

 the bars, in the dorsal valve twice as large as in the ventral valve. 



DimeTisioiis. — Diameter of the shell 0"24 to 0'28. 



Hahitat. — Central Pacific, Stations 270 to 274, surface, and at various depths. 



2. Conchidium thecidium, n. sp. (PL 124, fig. 6). 



Shell subspherical, slightly compressed on both sides. Dorsal valve somewhat smaller than 

 thp ventral, of simdar form. Principal axis of the shell somewhat longer than the sagittal, and this 

 longer than the frontal axis. Margins of the valves smooth in the oral quarter, strongly dentate 

 in the remainder ; on each side of one valve eight or nine very large triangular teeth, half as 

 long as the height of the valve. Aboral hinge with two unequal, stout, four-sided pyramidal horns ; 

 the dorsal horn half as long at the ventral. JMouth with two unequal lips, the upper shorter than 

 the lower. Pores of the sheU subregular, hexagonal, three to four times as broad as the bars. The 

 figured specimen, well preserved, contained in the central capsule two nuclei, one in the dorsal, the 

 other in the ventral half. 



Dimensions. — Length of the shell 0-28 to 0-33, height 0-27 to O'S, breadth 0-22 to 0-24. 



Habitat. — South Pacific, Station 292, depth 1600 fathoms. 



1 Conc^MiiMm = Similar to a bivalved mollusc ; ko'/x'^"'"- 

 (ZOOL. CHALL. EXP. — PART XL. — 1886.) Rr 216 



