REPORT ON THE HEXACTINELLIDA. 243 



oxypentacts, which form the main support of the dermal, gastral, aud canalicular 

 skin, and -which here and there appear to lie quite within the parenchyma, are really to 

 be regarded as true parenchymalia, does not seem to me probable. As a rule I could 

 readily connect them with the above named surfaces, and thus regard them as hypo- 

 dermal, hypogastral, and hypocanalicular elements respectively. 



The dermal skeleton has for its supporting basis large, strong oxypentacts, in which the 

 four long smooth tangential rays are usually indeed all but straight and crossed at right 

 angles, though not unfrequently somewhat curved, and in their inclination to one another 

 more or less diverted from a right angle. They are frequently disposed not exactly 

 tangentially, but slightly inclined inwards. The likewise long and strongly developed, 

 smooth, straight, proximal ray is, as a rule, at right angles to the surface ; it may, however, 

 in certain cases, for instance in the immediate neighbourhood of the marginal boundary, 

 deviate from this exactly radial disposition. The tangential rays of the adjacent 

 hypodermal pentacts lie for the most part in long stretches close to one another, and thus 

 form a strong, quadratic, dermal lattice- work, in the meshes of which the sieve network of 

 the dermal membrane is spread out. The quadratic skeletal meshwork is, however, in no 

 way uniformly composed, but numerous deviations and displacements occur all over. 

 The skin is externally beset with autodermal pentact pinuli which are more or less rough- 

 ened. Their tangential basal rays are of considerable length and almost always smooth, 

 but rarely tuberculate towards the end, while the moderately long (0"15 to 0"2 mm.) 

 radially projecting distal is smooth below, but on the outer three-fourths of its length 

 beset in fir-tree-like fashion with strongly developed lateral spines (PI. XLIII. fig. 4). 

 It is noteworthy that these dermal pinuli are in no way so abundantly or thickly present 

 as is usual in the other Hyalonematids ; in certain positions, indeed, they are sparsely 

 present or have a quite isolated occurrence. Especially near the oscular margin they are 

 only to be found here and there among the especially abundant pleural prostalia 

 (PL XLIII. fig. 2). 



As to amphidiscs, I found, in the external skin of the North Atlantic specimens, 

 only the small (0-03 to O'OS mm.) eight-rayed form (PI. XLIII. figs. 6, 8) with short 

 hemispherical umbels. In the remains of the Brazilian specimens, however, besides the 

 above forms, larger eight-rayed amphidiscs of similar form (PL XLIII. figs. 9, 10) 

 occurred. I hesitate, however, before proposing to erect a distinct species on the strength 

 of this single deviation. 



In the compact gastral membrane the skeletal elements are disj^osed in essentially the 

 same way as in the external skin. The following deviations are, however, of some 

 interest. In the first place, the whole free surface is much more closely and uniformly 

 beset with pinuli, and these pinuli differ from the autodermal forms in this, that 

 they are for the most part, especially in the neighbourhood of the oscular opening, 

 bent by the stream of water towards the efferent aperture (PL XLIII. fig. 2). The 



