EEPORT ON THE RADTOLAEIA. 1163 



Genus 514. Litharachnium,^ Haeckel, 1860, Monatsljer. d. k. preuss. Akad. d. 



Wiss. BerliD, p. 835. 



Definition. — Ar cliiphormida (vel Monocyrtida multiradiata aperta) wth flatly 

 conical, tent-shaped or nearly discoidal shell, and numerous, simple, radial beams in its 

 wall. 



The genus Litharachnium, and the closely allied genus Cladarachnium, differ from 

 the preceding similar genera mainly in the flat form of the depressed shell, which is not 

 slenderly pyramidal, but more tent-shaped or nearly discoidal. The radial ribs are 

 generally not straight, but more or less curved. The top of the tent exhibits three or 

 four important meshes, the original pores of the cortinar septum. Litharachnium may 

 be derived directly from Sethophormis by reduction and loss of the cephalis. 



Subgenus 1. Litharachnidium, Haeckel. 



Definition. — Apex with three cortinar pores (one odd sternal and two paired cardinal 

 pores). 



1. Litharachnium tentorium, Haeckel. 



Litharachnium tentorium, Haeckel, 1862, Monogr. d. Radiol., p. 281, Taf. iv. figs. 7-10. 



Shell flatly conical or tent-shaped, with concave lateral outhues. Apex with three equal 

 cortinar pores. Twenty radial ribs at nearly equal distances. Between them very numerous and 

 thin secondary ribs, crossed by more than one hundred concentric rings. Pores square, as in all 

 the following species. Margin truncate, circular. 



Dimensions. — Shell 0"35 long, O'S broad. 



^aSito^.— Mediterranean (Messina). 



2. Litharachnium araneosum (PL 5^, figs. 8, 10). 



Shell flatly conical, nearly discoidal, with straight lateral outlines. Apex with three unequal 

 cortinar pores (one odd smaller sternal and two paired larger cardinal pores). Twenty radial ribs 

 at unequal distances, with numerous intercalated secondary ribs. Margin ciliate. 



Dimensions. — Shell 0'18 long, 0'32 broad. 



Habitat. — Central Pacific, Station 271, surface. 



' iii/iarocA7iiuni= Spider-web of silex ; Ai^o^, dod^mo . 



