452 PROr. p. MAETIN DUNCAN ON THE 



The nature of the poriferous zone does not separate the genera. 

 It is evident that every specimen of Temnopleurus presents cre- 

 nulation of its primary tubercles, although it is often indistinct 

 in some parts of the test. The tubercles of JPleurecJiinus, when 

 carefully examined, do not show crenulation any more than 

 specimens of Temnechinus, Forbes. What is seen in improperly 

 denuded tests are the relics of the soft tissue which extended 

 over the boss to the ring of the spine. 



The examination of the construction of the test of PleurecMnus 

 lothryoides should prove the classificatory position of the form 

 in relation to the genera Temnopleurus and Temnechinus ; and this 

 proceeding was possible from the kindness of Dr. Griinther, F.R.S., 

 of the British Museum. Several specimens of Pleurechinus 

 hothryoides are in the National collection. One, a denuded test, 

 has been in the collection for years, and doubtless is a fellow of 

 the type in Paris ; others were dredged by the ' Alert ' in the 

 Japanese seas, and there are the specimens collected by H.M.S. 

 ' Challenger.' Dr. Griinther gave me his sanction to utilize one 

 of the specimens, and I chose one of the forms from the * Alert ' 

 collection. The first examination of the outside of the test 

 enabled me to admire A. Agassiz's description and drawings of 

 the species ; the second proved that the smallest and almost 

 miliary tubercles near the sutural depressions carried long stalked 

 pedicellarise resembling those of Temnopleurus, and that there 

 were globose, slightly elongated sphseridia on short stalks at the 

 edge of the actinal sutural depressions close to the peristome. 



The third examination consisted in carefully breaking asunder 

 the coronal plates and separating them from the poriferous zones 

 of the ambulacra. This was done with the view of determining 

 whether the test had true pits passing inwards and undermining 

 the test at the sutural angles, besides the sutural depressions, 

 which are such marked features and are usually called pits ; also 

 to make out whether or not there was any knob-and-socket 

 suturing along the median line of the plates, and also on the hori- 

 zontal edges actinally and abactinally. In fact, I was desirous 

 to discover whether the form had any structural relations with 

 Temnopleurus, Sahnacis, and Amhlypneustes *. 



All the structural characters of the sutures of Temnopleurus 

 were found in Pleurechinus hothryoides, more or less modified. 

 The depressions along the lines of horizontal sutures, called by 



* Journal of the Linuean Society (Zoology), vol. xvi. 1882, p. 343, pi. viii. 



