Page:Scientific results HMS Challenger vol 18 part 1.djvu/840

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 Larnacillida) 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."

Synopsis of the Genera of Pylonida.

III. Subfamily Haplozonaria. One system of girdles. Medullary shell simple, spherical or lentelliptical; cortical shell simple, with one, two, or three girdles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell only with one latticed (transverse) girdle,			279. Monozonium.
		Cortical shell with two perfect girdles (transverse and lateral),			280. Dizonium.
		Cortical shell with three perfect girdles (transverse, lateral, and sagittal			281. Trizonium.
III. Subfamily Diplozonaria. Two systems of concentric girdles. Medullary shell trizonal, with three perfect girdles; cortical shell simple, with one, two or three girdles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell only with one perfect (transverse) girdle,			282. Amphipyle.
		Cortical shell with two perfect girdles (the transverse and lateral).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Four gates simple,	283. Tetrapyle.
				Four gates bisected by a sagittal septum,	284. Octopyle.
		Cortical shell with three perfect girdles (transverse, lateral, and sagittal),			285. Pylonium.
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.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Outer cortical shell (third system) only with one perfect (transverse) girdle,			286. Amphipylonium.
		Outer cortical shell with two perfect girdles (transverse and lateral),			287. Tetrapylonium.
		Outer cortical shell with three perfect girdles (transverse, lateral, and sagittal),			288. Pylozonium.

Subfamily 1. Haplozonaria, Haeckel.

Definition.—Pylonida with one single system of fenestrated girdles (with one, two, or three girdles, lying in one lentelliptical face).