REPORT ON THE RADIOLARIA. 625 



Genus 276. Larnacoma,^ ii. gen. 



Definition. — L a v u a (• i d a with double leutelliptical cortical shell, without radial 

 spines. Medullary shell double, Zar»ac?7/(? -shaped. 



The genus Larnacoma has originated from the nearly allied Larnacalpis by 

 duplication of the cortical shell. Whilst in both genera the connection between the 

 ZarnctcfZ/a -shaped medullary shell and the primtiry cortical shell is the same, many short 

 radial beams arise from the surface of the latter in Larnacoma, which at constant equal 

 distances from it unite l)y a network forming the secondary or outer cortical shell. 

 It differs from the similar Druppulida (yCromyodruppa) hj the sagittal flattening of 

 the lentelliptical shell and the La rnacilla -form of the double medullary shell. 



1. Larnacoma lentellipticum, n. ,sp. 



Shell with .smooth surface and elliptical perimeter, one and a third times as long as broad. All 

 four shells lentelliptical. Distance between the two cortical shells about twice as great as the 

 distance of the inner cortical and outer medidlary shell. Network of both outer shells irregular, 

 with large roundish pores, twice to six times as broad as the bars. 



Dimensions. — Length (or principal axis) of the first (innermost) shell O^Oo, second 0'08, 

 third 0"16, fourth (outermost) 027, breadth (or transverse axis) corresponding — ^(A) 0"02, (B) 0'05, 

 (C) 0-11, (D) 0-2. 



Habitat. — South Atlantic, Station ?>'!?<. depth 19l)(l fathoms. 



2. Larnacoma quadruplex, n. sp. 



Shell with thorny surface and elliptical perimeter, one antl a fifth times as long as broad. All 

 four shells lentelliptical. Distance between the two cortical shells somewhat smaller than the 

 distance between the inner cortical and outer medullary shell. Network of both outer shells 

 irregular, with large roundish pores, twice to ten times as broad as the bars. 



Dimensions. — Length of the first shell 0-02, .second O'Ofi, third (>15, fourtii 0'24; breadth 

 corresponding— (A) 016, (B) 0-04, (C) Oil, (D) 0-2. 



Habitat. — South Atlantic, Station ?>o5, depth 142."> fiithoms. 



3. Larnacoma hexagonium, n. s\x 



Shell with thorny surface and he.xagonal perimeter, as long as broad. All four shells hexagonal, 

 connected by six *[iiercing radial beams (two in the principal axis, four others in two crossed diagonals). 

 Distance between the two cortical shells somewhat gi-eater tlian the distance between the outer 

 cortical and inner medullary shell. Network of both outer shells subregidar, with small circular 

 pores, twice as broad as the bars. 



1 /.o?-7!ncoma = Shell of chest form; XajKaf. 

 (ZOOL. CHALL. EXP. — P.\nT XL.— ISS.'i.) Rr 79 



