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



6. Pylonium stenozonium, n. sp. 



Cortical shell thorny, with eight short conical radial spines, lying in two crossed diagonal planes 

 (as in the foregoing species). All three girdles nearly of the same size, subcircular, very narrow, 

 only with one to two rows of pores. Four gates kidney-shaped. 



Dimensions. Principal axis 015, transverse axis 014 ; diameter of the quadrangular medullary 

 shell 0-04 



Habitat. Equatorial Atlantic, Station 347, surface. 



Subfamily 3. TRIPLOZONARIA, HaeekeL 



Definition. Pylonida with three concentric systems of fenestrated girdles, lying 

 in three concentric lentelliptical faces (every system with one to three girdles lying in 

 one lentelliptical face). 



Genus 286. Amphipylonium, 1 Haeckel, 1881, Prodromus, p. 463. 



Definition. P y 1 o n i d a with trizonal lentelliptical medullary shell, surrounded by a 

 double latticed cortical shell ; inner cortical shell Pylonium-shaiped, with three perfect 

 crossed girdles; outer cortical shell only represented by a single (transverse) girdle. 



The genus Amphipylonium opens the series of Triplozonaria, or of those Pylonida 

 in which the shell is composed of three concentric systems of latticed girdles. The first 

 (and innermost) system represents the complete trizonal medullary shell, which is 

 probably a lentelliptical Larnacilla-shell. The first and intermediate system is formed 

 of a complete trizonal cortical shell of the same form, but much larger (like Pylonium). 

 The third (and outermost) system is represented by one to three latticed girdles, corres- 

 ponding to the former and forming an outer or second cortical shell. In Amphipylonium 

 (as the most simple form of the Triplozonaria) there is only developed the first (transverse) 

 girdle of the third system. It repeats therefore the form of Amphipyle, the cortical shell 

 of which is here double (Prodromus, 1881, p. 463). 



1. Amphipylonium semilunare, n. sp. 



Inner cortical shell lentelliptical, one and a half times as long as broad, with smooth surface and 

 four semilunar gates. Transverse girdle of the outer cortical shell with two smooth semilunar 

 wings, with convex, smooth lateral crests; each wing as broad as the transverse girdle of the inner 

 cortical shell and twice as long as its lateral girdle. 



Dimensions. Length of the lentelliptieal medullary shell 0'04, breadth O03; length of the 

 inner cortical shell 015, breadth 01; length of each lateral wing of the outer cortical shell 0'3, 

 breadth 01. 



Habitat. Pacific, central area, Station 271, depth 2425 fathoms. 



1 Amphipylonium = With one large gate on either side ; *(t$i, w\u>itm. 



