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



margin. The month-plates are small and inconspicuous, and each plate bears on its adoral 

 margin two small mouth-spines. The inner pair are directed horizontally over the buccal 

 membrane and are parallel to one another and the median interradial line ; the outer pair, 

 which are at the outer extremity of the adoral margin of the plates, are likewise directed 

 horizontally over the buccal membrane, but outward, forming an angle of about 45° to the 

 inner mouth-spine. These marginal mouth-spines are less than 1 mm. in length, are 

 covered with delicate membrane, and bear at the tip a number of small pedicellarise. Each 

 plate bears on its actinal surface a secondary or superficial mouth-spine, about 5 mm. in 

 length, articulated on a prominent tubercle, and encased in a membranous sheath bearing 

 large pedicellarise. 



The madreporiform body is small, convex, subtubercular, situated very near the abactinal 

 margin of the disk ; its surface is marked with but few, widely-spaced, striation-furrows. 

 A distinct anal aperture is present, and its position is excentric. 



Colour in alcohol, a bleached yellowish ashy grey, with a slight tendency to a bight 

 brownish shade, especially on the ovarial regions. 



Locality. — Station 184. Off Torres Strait, Pacific side. August 29, 1874. Lat. 

 12° 8' 0" S., long. 145° 10' 0" E. Depth 1400 fathoms. Globigerina ooze. Bottom 

 temperature 36°"0 Fahr. ; surface temperature 77 0, 5 Fahr. 



Remarks. — This species is nearly related to Freyella echinata, of which the echinulate 

 forms might easily be considered at first sight as a variety. The general habit, however, 

 of the two starfishes is different in many respects, notwithstanding their apparent nearness 

 in several points of numerical formula, and when the unarmed forms are had in view there 

 is very little in their superficial aspect that would recall Freyella echinata. In Freyella 

 dimorpha the number of rays is twelve, and this appears to be fairly constant, whereas 

 in Freyella echinata there are usually eleven. In Freyella dimorpha they are propor- 

 tionately longer as well as more delicate and attenuate, whilst the ovarial regions are of 

 less extent. The numerous small spinelets on the abactinal plated area are quite different 

 from the armature of those plates in Freyella echinata. In Freyella dimorpha the lateral 

 spines are considerably longer, although the species is relatively smaller, and their delicacy 

 is exceptional. In this form the true or marginal mouth-spines are small, and their mem- 

 branous investment as well as the grouping of the pedicellarise thereon is different. The 

 saddle-like sacculi upon the abactinal membrane of the ray beyond the ovarial region 

 are broader and also maintain their breadth across the median abactinal keel. 



Although these differences may appear small in description, they represent variations 

 of character which I find to be fairly constant in species, and on these grounds I have con- 

 sidered the forms under notice as worthy of separate recognition. The dimorphous 

 character of this species, some forms being echinulate and others not, is remarkable. The 

 species also presents some resemblance, perhaps mimetic, to Freyella fragilissima and 

 Freyella bracteata. 



