Page:Scientific results HMS Challenger vol 18 part 1.djvu/515

of a double medullary shell (Pl. 39, fig. 4). From these two genera all other forms of the subfamily may be derived.

The Central Capsule of the Druppulida is constantly ellipsoidal, larger than the concentric enclosed medullary shells, smaller than the surrounding cortical shell; it is separated from the inner surface of the latter by a thinner or thicker jelly-mantle.

Synopsis of the Genera of the Druppulida.

Cortical shell without polar appendages (neither solid spines nor hollow tubes at the poles of the main axis).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell simple, ellipsoidal.			$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Medullary shell simple.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Surface smooth,	131. Druppula.
								Surface spiny,	132. Druppocarpus.
						Medullary shell double.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Surface smooth,	133. Prunulum.
								Surface spiny,	134. Prunocarpus.
		Cortical shell composed of two or more concentric shells.			$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right\}\,}$	Medullary shell double.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Surface smooth,	135. Cromyodruppa.
								Surface spiny,	136. Cromyocarpus.
Two opposite solid spines, arising from the poles of the main axis.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell simple, ellipsoidal.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Medullary shell simple.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Both polar spines equal,			137. Lithatractus.
						Both polar spines unequal,			138. Druppatractus.
				Medullary shell double.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Both polar spines equal,			139. Stylatractus.
						Both polar spines unequal,			140. Xiphatractus.
		Cortical shell composed of two or more concentric shells; medullary shell double; both polar spines equal,							141. Cromyatractus.
Two opposite hollow fenestrated tubes, arising from the poles of the main axis.	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	Cortical shell ellipsoidal.			$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,			142. Pipetta.
						Medullary shell double,			143. Pipettaria.

Genus 131. Druppula,^[1] n. gen.

Definition.—Druppulida with simple ellipsoidal, cortical shell, and simple medullary shell, without spines or polar tubes.

The genus Druppula, as the simplest form of the Druppulida, may be regarded as the common ancestral form of this subfamily. It may be derived phylogenetically either

1. Druppula = Small drupe or δρύππα, ripe Olive.