AULOSACCÜS MITSUKURII. 119 



ber of broad-based conical prominences, the conuli, that rise from 

 the external surface. These are most prominent in the middle 

 part of the body, reaching 10 mm. or more in height as mea- 

 sured from the depressed surface between them. Their apices 

 are generally 10-30 mm. apart from one another. Their appear- 

 ance reminds one at once of the conuli of Acanthascus cactus. 

 The resemblance is all the greater since they bear on the apices 

 thin prostal needles directed either straight outwards or obliquely 

 upwards. Usually a single prostal occurs on each conulus, but 

 there are sometimes more than one. It may project to a length 

 of 15 mm. In the immediate neighborhood of the oscular mar- 

 gin there exist some upwardly directed prostals that arise without 

 a conical elevation of the wall at their base. 



Strikingly similar as is the general external appearance be- 

 tween this species and Acanthascus cactus, a close comparison 

 reveals certain points of difference in the structure of the ecto- 

 somal skeleton, — differences, which, under certain circumstances, 

 might suffice to distinguish the two species upon superficial obser- 

 vation alone. In the first place, the delicate dermal lacework 

 of the present species allows the meshes, minute though they f^i'e, 

 to l^e perceived without difficulty with the naked eye, while for 

 A. cactus the same can hardly be said. This is owing to the 

 difference in the thickness of the rays of their dermalia. In the 

 next place, the supporting hypodermal strands are considerably 

 fewer. Thev intersect one another at various angles and form 

 triangular, trapezoidül or irregular meshes, the sides of which 

 not infrequently measure 4 mm. or more in length. Whereas, 

 the same meshes in A. cactus (PL XL, fig. 17) rarely, if ever, 

 exceed Ih mm. In short, the hypodermal framework of the pre- 



