72 Prof. P. M. Duncan on the Salenidas. 



this first communication two morphological points, one of 

 which bears on the question of classification to a certain extent, 

 and the other adds to our knowledge of the structures of the 

 appendages of the test. 



The specimen of a recent Salenia which I have studied is 

 in the possession of Prof. Huxley, and was dredged up during 

 the expedition of H.M.S. ' Challenger'; owing to his kind- 

 ness I have been permitted to wash the apical disk carefully 

 and to examine the form at ray leisure. The specimen has 

 its extraordinary spines upon it, and the actinal membrane is 

 preserved ; the apical disk is perfect, and the relative position 

 of the permanent anal plate can be decided. 



On careful and gentle washing under a microscope, much 

 mud and Globigerince were removed from the peristome and 

 anal plate and membrane. The result was that sphgeridia 

 were noticed in each ambulacrum ; and short-stemmed globose- 

 headed pedicellariee, like those seen on the actinal membrane 

 by A. Agassiz, were found distributed along the ambulacra be- 

 tween the rows of spines, and almost invariably between the 

 numerous blunt spines of the apical disk. They were noticed 

 also sparingly in the interambulacra. 



The sphffiridia of this Salenia (a variety of 8. varispina ?) are 

 to be found in each ambulacrum ; two are situate between the 

 spines nearest the peristome and its edge, one in advance of 

 the other, and they are flanked by the last two tentacles, 

 which are rather convergent. The sphseridia are unequal 

 in size, but have an elongated globose shape, not very unlike 

 a stout form of those of Sti^ongylocentrotus drohachensis. Each 

 is placed on a short and narrow stem, and is seated on a 

 minute tubercle, and the smaller one is nearest to the smallest 

 terminal spine of the ambulacrum. They are brilliantly 

 glassy in appearance, and a faint longitudinal striation and a 

 pigment-spot are visible on some. They are strikingly visible 

 over the granular test, which has minute pigment-spots; and 

 (considering that the Salenia only measures ^ inch across the 

 test) they are large. One other sphteridium is visible slightly 

 higher up, and just within the range of the pores and external 

 to the larger ambulacral spines. It is longer and larger than 

 the others, but presents all the usual characters of these inter- 

 esting structures. In height the medium-sized sphaeridium 

 is about ^^ inch, and is rather less thick than the smaller 

 globose-headed pedicellariss ; but its short graceful stalk and 

 base are very much shorter than those of these last-mentioned 

 appendages to the test. The sphaeridia and pedicellarise are 

 less transparent than in Strongylocentrotus. 



In noticinsr tlie different characters which are common to 



