256 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Daidcdometra hana. — There appears to be no essential difference between the 

 side and covering plates of this species and those of Stenometra quinquecostata. 



Parametra orion. — The side plates are of two types ; the larger, with the cover- 

 ing plates, resemble those of Oceanovietra gigantea; just at the distal border of 

 these large side plates, and covered by the oasal portion of their distal edges, are 

 much narrower side plates of the same length, which in lateral view appear as 

 long rods making an angle of something over 60° with the border of the pinnulars. 

 AVhile they appear rod like in lateral view, the distal third of these plates is 

 abruptly produced inward, at right angles to the longitudinal axis of the pinnule, 

 for a distance equal to somewhat more than the length, the distal border of this 

 process being convex and often a semicircle. In direct ventral view, this expanded 

 portion is seen to be slightly convex distally. The basal edge of the side plates 

 is parenthesis shaped in end view. 



Parametra granulata (figs. 874-878, p. 435). — The side and covering plates 

 resemble those of P. orion. 



Oceanometra gigantea (figs. 859-866, p. 419). — In this species there are two 

 rows of side and covering plates, one, composed of much the larger and more per- 

 fect plates, superficial, the other, composed of smaller and less perfect plates 

 alternating with these, situated in the deeper perisomic layers. 



In lateral view the larger side plates, those of the superficial series, are 

 trapezoidal ; the distal border, which is straight and perpendicular to the pinnulars, 

 is somewhat longer than the base; the proximal border is half again as long; the 

 outer border is convex, with the median third produced and its outer edge concave, 

 so that it usually takes the form of two obtuse angles. The inner half of the 

 plates is plane, but in their outer halves they twist in such a way that the outer 

 border makes an angle of approximately 45° with the base, the proximal outer 

 angle, which is more or less strongly rounded, being inward ; on the proximal side 

 at about the level of the obtuse angle between the distal and outer sides is a 

 rounded notch. 



The covering plates, which are broadly oval, slightly longer than broad, are 

 attached just within the proximal outer angle. 



Alternating with the side plates just described and deeply sunken within the 

 perisome are large definite groups of spicules of all shapes and sizes, more or less 

 agglutinated and sometimes becoming very irregular plates, which are separated 

 by intervals of somewhat more than their own longitudinal diameter, or the diame- 

 ter parallel with the border of the pinnulars, which is usually greater than the 

 diameter at right angles to the border of the pinnulars. 



Beyond these, and entirely separated from them, are much more definite 

 sausage-shaped covering plates, leaning distally at an angle of about 60° with the 

 edge of the pinnulars, their outer ends reaching to, or slightly beyond, the bases of 

 the larger covering plates. 



The perisome over the genital glands is completely inclosed by longitudinally 

 elongate plates, which decrease rapidly in size from the pinnulars to the side plates. 



The tentacles may contain extremely minute deposits, especially toward 

 their tips. 



