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



The principal spicules of the parenchymal skeleton are slender, smooth diacts, of 

 varied length. They exhibit rough ends thickened in club-like fashion. Less frequently 

 simply rounded or pointed diacts occur. Many of these long diacts exhibit no swellings 

 or lateral processes at their middle point, while others bear four cruciate, or two opposite 

 tubercles — the rudiments of undeveloped rays. 



Between these long jiarenchymal spicules a large number of irregularly scattered 

 oxyhexastere occur. They exhibit strongly developed, short principal rays, and two to 

 four long, straight, divergent terminals on each principal (PI. LXVI. fig. 6). It ought 

 to be noted that oxyhexasters very frequently occur in which one principal ray is con- 

 spicuously longer than the others, so that the whole sj^icule deviates considerably from 

 the rosette form. Other irregularities occur, such as the displacement of one of the 

 terminal rays from the common whorl to the side of the associated principal ; spinous 

 ramifications or irregular twistings occur here and there as abnormal, or perhaps as 

 pathological modifications (PI. LXVI. figs. 11, 12). In isolated cases, I observed disco- 

 hexasters with moderately short princijDal rays, bearing on their expanded ends numerous 

 long, thin terminals, radially disposed, and each terminating in a transverse disc with 

 clasp-like teeth (PI. LXVI. fig. 7). In the subdermal spaces of the connecting portion 

 between the stalk and the body, large discohexasters of floricome-like pattern occur, as 

 is also the case in Aulochone lilium (PI. LXVIII. fig. 5). The 2>erianth-like groups of 

 terminal rays are in this species, however, somewhat thinner at their basal and median 

 portions. 



The dermal skeleton consists of strongly developed rough pentacts, of variable size, 

 the rays having rounded or club-shaped ends. Between these pentacts, tetracts of similar 

 structure occasionally occur. The gastral skeleton on the upper funnel-like surface, and 

 on the cylindrical sides, consists of rough pentacts similar to the above (PL LXVI. 

 fig. 10). 



On the much curved regions, both dermalia and gastralia exhibit a backward curvature 

 of the four tangential rays. On the superficial side a small tubercle is occasionally seen 

 where the sixth ray has not been developed. 



In the skin which lines the large canalicular cavities of the body, I have never found 

 any special canalaria. 



The skeletal elements of the stalk do not essentially diff'er from those of the body 

 generally. The longitudinal and transverse, i.e., circular, bundles of spicules usually 

 alternate in their arrangement. Between the above, the oxyhexasters and small disco- 

 hexasters already referred to occur, while the large floricome-like discohexasters are found 

 more abundantly in the subdermal spaces. The dermalia are strongly developed, and 

 the inwardly projecting radial proximal ray is often strikingly shortened. The gastralia 

 are frequently less rough in their median portion, while the club-shaped thickened ends 

 always exhibit numerous minute spines. 



