350 PEOF. p. M. DUNCAN ON THE MORPHOLOGY 



IV. The Morpliology of the Pits, sutural marginal Grooves, and 

 Sutures o/' Temnopleurus toreumaticus, -4yass., 18il. 



The pits of all the areas are very visible in this t3'pical species 

 of the genus Temnopleurus ; and there are marginal sutural grooves 

 of a very distinct kind. The pits have a considerable inward 

 oblique and vertical extension within the test ; their inner dimen- 

 sion varies according to position ; and they occupy depressions in 

 the edges of adjoining plates. 



At the ambitus especially the principal tubercle of each inter- 

 radial plate, or a process of its scrobicule, comes close to the 

 actinal edge and covers and obliterates, to a greater or less extent, 

 the margmal grooving. So that wben the plate is separated 

 from the one below, or that which is placed orally to it, the base 

 of the tubercle, or a prolongation of its subscrobicular structure, 

 is seen to project into a concavity on the outer surface of this 

 lower plate close to the abactinal sutural part. 



This deep grooving of the sutural margin and of the superficies 

 of the test close to it, coupled with the existence of the great 

 primary tubercle with its basal structure, interferes with the 

 thickness of the actinal and abactinal edge of the plates. The 

 thickness is greatest in the central part of the edge, and thence 

 there is a gradual thinning on either side. The actinal edge of 

 each interradial plate is covered with numerous knobs, rounded at 

 the end, and of the same character as those noticed in Salmacis 

 sulcata. Sometimes the knobs are placed irregularly ; and in some 

 places they are in lines, and then one knob runs into another, and 

 a line of elevation is produced and is more or less continuous. 

 On the abactinal edge of the plates there are sockets which cor- 

 respond with the knobs and lines of elevation of the adjoining 

 plate. (Plate VIII. figs. 10 & 11.) 



In the ambulacral areas the median pits are deep, oblique, and 

 uot much expanded within. The grooving of the margin of the 

 sviture is very decided towards the median line, and less so towards 

 the poriferous zone ; and, in the first place, the thickness of the 

 plate is greatly reduced. Hence the outline of the horizontal 

 sutural edges of the ambulacral plates is irregular. The actinal 

 edge of each plate has numerous sockets, which receive the knobs 

 of the abactinal edge of the plate below. Thus there is the same 

 reversal of the direction of the knobs and sockets, with regard 

 to those of the interradial areas, as was noticed in Salmacis sul- 



