192 PBOF. p. MAETIN DUNCAJSr ON THE 



are the apertures of the second plate. (See the fig. 14 of Sal- 

 macis.) The pair of pores next to this last on the flank of the 

 process are close, and the outer or aboral pore is a long way off 

 the suture between the ridge and the process. The pair belongs 

 to a third plate, and its sutures are visible, under the effects of 

 benzene, betw^een it and the plates, nearer and further from the 

 peristome; but no suture can be traced towards the division 

 between the process and the ridge, and therefore the part of the 

 plate remote from the ambulacral median line merges into the 

 mass of the process, as in Balmacis. Tlie next pair of pores are 

 on the flank of the process which trends circumferentially, and 

 the pores are more distant than the others ; they belong to a 

 plate which is not separable from the process. The succeeding 

 pair of pores are wide ajDart, and they belong to a compound 

 plate, which has all the sutural lines visible under benzene, and 

 therefore this plate does not form a part of the foundation of 

 the process. Pour plates at least enter into the composition of 

 the base and upward-stretching parts of the process. 



The suture between the ridge and a process, when seen from 

 within the test, passes almost in a right line to reach the flat 

 upper surface of the actinal part of the test, just beyond the 

 slope of the ridge, and then it clearly becomes continuous with 

 the ambulacro-interradial suture. 



It must be understood that the position of the pairs of pores 

 on the flank of a process is very oblique, and that the direction 

 of what remains of their plates is upwards and sideways from 

 the direction of the median suture of the ambulacrum. This 

 uptilting enables the plates to add to the height and thickness of 

 a process. 



MicrocypTius zigzag, Agass. — This species has a thick test, and 

 the peristomial edge bends in, and although it is said Jiot to have 

 " cuts," they are as evident as are the small and narrow grooves 

 continuous with them on the inner side of the perignathic ridge. 

 The perignathic girdle is high, and the processes are rather 

 slender ; they are united by suture superiorly, and the space they 

 enclose is somewhat triangular. The base of a process and the 

 part formed by the first four or five ambulacral plates resembles 

 that of the Temnopleuridse already noticed. 



The ridges are tall and comparatively narrow, and the free 

 upper edge of each is curved downwards, or there may be 

 a projection on the edge at the median line (fig. 15). The 



