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



Tlie Medulla yy Shell is always double in tlii« familj-, composed of two small 

 concentric shells lying in the middle of the central capsule. Tliej^ are either spherical 

 or lenticular, comj)ressed towards Ijoth poles of the main axis ; sometimes the inner is 

 spherical, the outer lenticular. From the equatorial circumference of the latter starts a 

 number of radial beams, which perforate the central capsule, and are inserted into the 

 equatorial constriction of the cortical shell. Commonly all radial beams lie in the 

 equatorial plane, sometimes also a part of them on both sides of it. 



The Cortical Shell is constantly composed of four completely latticed chambers, 

 which are only separated l>y the three annular constrictions. In many species all four 

 chambers have the same form and size (PI. 40, fi,!;;. 3), but in the greater number of 

 sjaecies both proximal (or central) chambers are clifl'erent in size, shape, or structure from 

 both distal (or polar) chamliers. The cortical shell is either simple or double, composed 

 of two concentric four-jointed shells ; rarely it is triple or multiple, composed of three or 

 more shells fitting one inside the other. Very often the outer cortical shell is incomplete, 

 and only developed around the two proximal chambers of the complete inner cortical 

 shell, both distal chambers of the latter remaining simple. 



On both poles of the main axis often are develojsed solid spines {Panicium, PL 40, 

 fig. 4) or hollow fenestrated tubes {Panarmm, PI. 40, fig. 9), as in the foregoing families. 

 Besides this, the surface of the cortical shell may be armed with spines. 



The Central Capsule of the Panartida is always cylindrical, on both poles hemi- 

 spherical ; commonly it is more or less distinctly four-jointed, with three ring-like 

 constrictions corresponding to those of the enclosing cortical shell. From the inner 

 surface of the latter it is separated by a thinner or thicker jcUv-mantle. 



Si/nojxsis of the Genera of Panartida. 



On both poles of the main axis neitlier ( Cortical .shell tsimple, 

 peculiar polar spines nor fenestrated ■; 

 tubes. ( Cortical sbell double or triple, 



r\ -u ii ^ e n ■ ■ i ( Cortical shell simple, 



On both poles of the main axis a large | ' ' 



apical spine or a "roup of polar spines. I ,, .• , i ,, , i, , ■ , 

 ^ ' tn 1 i 1 ( Cortical shell double or triple, 



rv V i-t. 1 c ii • • ■ 1 ( Cortical shell siraiile, 



On both poles or the mam axis a conical | ' 



or cylindrical fenestrated tube. I n ^ i i u i 1 1 i • i 



■' [ Cortical shell clouble or triple. 



Genus 1G3. Panartus} n. gen. 



Definition. — P anar t i d a with simple cortical shell and double medullary shell, 

 without polar spines or tubes on both poles of the main axis. 



' /'nnariws = quite tiread-like ; Trii/a^os. 



16.3. Paimiiuii. 



1G4. Peripaiiiniiin. 



1G5. Panic! nm. 



16G. Pcrijiiiiiiciiini. 



167. Panariiiin. 



168. Peripaimrimii. 



