632 



THE VOYAGE OF H.M.S. CHALLENGER. 



inclination to individual abnormalities, formation of varieties and transitions into 

 other families, hence derived, as Larnacida, Tholonida, Lithelida, &c. 



The central capsule in all Pylonida, in which I could observe it, was a true 

 lentellipsis (or a " triaxial ellipsoid " in the geometrical sense, with the three unequal 

 isopolar axes of the " rhombic octahedron "). In the living Pylonida it is commonly 

 coloured pink or scarlet. During growth its dimensions are probably more or less 

 changed, and perhaps the axes alternate. Regarding the relation of the central 

 capsule to the skeleton, we can distinguish two different groups, quite as in the 

 nearly allied Larnacida. In the Haplozonaria (as also in the Laruacillida). the central 

 capsule encloses only the central chamber and is enveloped by the first system of girdles, 

 whereas in the Diplozonaria and Triplozonaria (as in the Larnacalpida) that " trizonal 

 shell " becomes enclosed (as the " medullary shell") in the central capsule, which is 

 now enveloped by the second system of girdles as the " cortical shell." 



I. Subfamily 



Haplozonaria. 



One system of girdles. 

 ' Medullary shell simple, 



spherical or lentelliptical ; 



cortical shell simple, with 



one, two, or three girdles. 



II. Subfamily 



Diplozonaria. 



Two systems of concentric 

 girdles. Medullary shell 

 trizoual, with three perfect 

 girdles ; cortical shell 

 simple, with one, two, or 

 three girdles. 



III. Subfamily 



Triplozonaria. 



Three systems of concentric 

 girdles. Medullary shell 

 trizonal, with three perfect 

 girdles, quite as the 

 inner cortical shell ; outer 

 cortical shell with one, two, 

 or three girdles. 



Synopsis of the Genera of Pylonida. 



Cortical shell ouly with one latticed (transverse) girdle, 



Cortical shell with two perfect girdles (transverse and 

 lateral), ..... 



Cortical shell with three perfect girdles (transverse, 

 lateral, and sagittal), 



Cortical shell only with one perfect (transverse) girdle, 



Cortical shell with two [ F Ur gat S aim ^ 

 perfect girdles (the trans- j Four bisected b 



verse and lateral). 



Cortical shell with three perfect girdles (transverse, 

 lateral, and sagittal), .... 



Outer cortical shell (third system) ouly with one perfect 

 (transverse) girdle, ..... 



Outer cortical shell with two perfect girdles (transverse 

 and lateral), ..... 



Outer cortical shell with three perfect girdles (trans- 

 verse, lateral, and sagittal), 



279. Monozonitmt. 



280. Dizoniinn. 



281. Trizonium. 



282. Amphipyle, 



283. Tetrapyle. 



284. Odopjlv. 



285. Pylanium. 



286. AmlnpyloniuHi . 



287. Tctrapylonium. 



288. Pt/lozonium. 



Subfamily 1. HAPLOZONARIA, Haeckel. 



Definition. P y 1 o n i d a with one single system of fenestrated girdles (with one, 

 two, or three girdles, lying in one lentelliptical face). 



