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



five, but may amount to nineteen, to twenty -one or more ; they lie constantly in pairs 

 on both sides of the equatorial constriction (PI. 40, figs. 12, 13). 



The cortical shell may either remain simple (Ommatocampe, PI. 40, fig. 10), or 

 become double (Desmocampe, PI. 40, fig. 12), or sometimes triple (Zygocampe, 

 (PL 40, fig. 13). In the latter cases the outer (secondary and tertiary) cortical shells 

 are commonly incomplete, and only developed around the proximal chambers of the 

 complete first (primary) cortical shell, its distal chambers remaining simple. 



The Medullary Shell is constantly double, as in the Pauartida ; its form is either 

 spherical or lenticular, compressed in the direction of the main axis. It is always 

 connected with the equatorial constriction of the cortical shell by a number of 

 radial beams, lying either in the equatorial plane or on each side of it (PI. 40, 

 figs. 10-13). 



The Central Capsule of the Zygartida is constantly cylindrical ; its increasing- 

 growth on both poles of the axis corresponds to that of the including cortical shell. 

 Commonly (but not always) its cylindrical surface is annulated, with five or more 

 transverse strictures, corresponding to those of the cortical shell. From the inner 

 surface of the latter it is separated by a jelly-mantle, the calymma, 



Synopsis of the Genera of Zygartidn. 



., { Without polar tubes, .... 169. Ommatocampe. 



I. Ommacampida. 



1. Cortical shell simple i w - fa tw(j h Uow fenegtrated tub on the les 



(Medullary shell double.) [ of tho axis> . . . 170 . Ommatartu*. 



., f Without polar tubes, . . . .171. Desmocamjti: 



II. Desmocampula. 



2. Cortical shell double. 1 wi fa t hollow fenestrated tubes, on the poles 



(Medullary shell double.) [ of the axig) . . 172 . Dcmiartus . 



III. Zygocampida. [ Without polar tubes, . 173. Z.jgocamp,: 



3. Cortical shell triple i h u fenestrated tubes, on the 

 (Medullary shell double.) , ,, -i^t v , 



' [ poles of the axis, . . . .174. Zijfjartus. 



Genus 169. Ommatocampe, 1 Ehrenberg, 1860, Monatsber. d. k. preuss. 

 Akad. d. Wiss. Berlin, p. 832. 



Definition. Z ygartida with simple cortical shell and double medullary shell, 

 without polar tubes. 



The genus Ommatocampe was founded by Ehrenberg in 1860 for one of his " Haliom- 

 matina," with the following diagnosis : " Shell rod-like, long, articulate, with nucleus, 

 without spines, with four or more joints." The species figured by him, Ommatocampe 



1 Omnuttocampe = Caterpillar with eyes; iy.ftx xxftw?. 



