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



Genus 274. Larnacalpis, 1 n. gen. 



Definition. Larnacida with a simple lentelliptical cortical shell, without radial 

 spines. Medullary shell double, Larnacilla-shapeA. 



The genus Larnacalpis represents the most simple form of the sub-family Larnacal- 

 pida, and is very important as the common original form of all those Larcoidea in which 

 a double Larnacilla-shaped medullary shell is surrounded by a simple, perfectly closed, 

 latticed, lentelliptical cortical shell. Therefore the same typical, trizonal, lentelliptical 

 shell, which in Larnacilla represents the external envelop (or cortical shell) of the 

 central capsule, here in Larnacalpis becomes enclosed as an internal nucleus (or medullary 

 shell) in the interior of the central capsule, and this latter becomes overgrown by a new 

 lentelliptical cortical shell. The connection between the two shells of Larnacalpis is 

 either effected by a number of radial beams (e.g., in Larnacalpis triaxonia by six beams 

 situated in the three dimensive axes), or by two lateral, latticed, tube-like wings, which 

 are repetitions of the smaller lateral wings connecting its external shell with the internal 

 medullary shell (as in Larnacalpis lentellipsis). The latter species may be regarded as a 

 Pylonium with a completely latticed shell. 



1. Larnacalpis lentellipsis, n. sp. (PL 50, figs. 2, 2a, 26). 



Cortical shell with thorny surface and irregular network ; pores roundish, twice to four times 

 as broad as the bars ; about sixteen on the half meridian, twelve on the half equator. Proportion 

 of the three dimensive axes = 2:3:4. Medullary shell one-third as large as the cortical, with four 

 elliptical internal gates, connected with it' by two opposite beams in the principal axis and by 

 two latticed wings in the transverse axis; therefore between the two shells are four large kidney- 

 shaped gates, halved by the polar beams (as in Octopyk). 



Dimensions. Length of the cortical shell (or principal axis) 014, breadth (or transverse axis) 

 O'll, height (or sagittal axis) 0'07 ; pores O'Ol to 0'02, bars O'OOo; length of the medullary shell 

 0-05, breadth 0'04, height O03. 



Habitat. Pacific, central area, Station 272, depth '2600 fathoms. 



2. Larnacalpis phacodiscus, n. sp. 



Cortical shell with thorny surface and regular network ; pores circular, twice as broad as 

 the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes 

 = 2 : 2'5 : 3. Medullary shell half as large as the cortical, witli four kidney-shaped internal 

 gates. 



Dimensions. Length of the cortical shell - 13, breadth O'll, height 0'09 ; pores 0'012, bars 

 0-006; length of the medullary shell 0'06, breadth 0'045, height 0'03. 



Habitat. North Pacific, Station 253, depth 3125 fathoms. 



1 Larnacalpis Tankard-shaped chest; AajxaJ, xaXr/c. 



