676 Proceedings of the Royal Irish Academy. 



Ploesoma lenticulare — continued. 



and overlapped by the neck-shield, as has been already described, 

 ■while posteriorly they join the dorsal areas already enumerated. 

 These lateral portions may further be described as each consisting 

 of a dorso-lateral and a ventre -lateral part separated from one 

 another by a prominent longitudinal ridge (r) which extends from 

 the neighbourhood of the outer angle of the neck- shield back to the 

 posterior apex of the lorica. The narrovT" dorso-lateral region is 

 marked by two other longitudinal ridges approximately parallel to 

 the boundary ridge (r), and is thus divided into three longitudinal 

 grooves, of which the most dorsal (/) is a mere shallow depression, 

 and scarcely extends further forward than the median transverse 

 furrows, while the other two (c, d), are well defined and run 

 forward towards the sides of the anterior dorsal plate. Each 

 ventro-lateral portion is traversed by three slight sinuous ridges, 

 which spring from a small central area in which is lodged the 

 lateral antenna, and run respectively to the dorso-lateral, ventral, 

 and oral margins. 



Foot ventral, annulate, with two toes. Corona nearly 

 uniform posteriorly, but with three larger tufts of cilia on the 

 ventral side. Two large retractile frontal horns. Three antennae, 

 of which one perforates the anterior dorsal sliield immediately in 

 front of the transverse median grooves, and the others perforate 

 the middle of the ventro-lateral portions of the lorica. Eye, 

 dark-coloured beneath the anterior dorsal shield. Mastax large ; 

 trophi forcipate. Length of the lorica about y+o i*i- 



Our figures of this E-otifer are, in so far as regards the char- 

 acters of the lorica, entirely the work of Mr. C. Eousselet, the 

 other structures represented being reproduced from drawings by 

 Mr. Dixon-Nuttall. Mr. Eousselet remarks that the animal is 

 exceedingly difficult to draw ; its complicated contours make it 

 almost impossible to render accurately in any one view the 

 arrangement of the grooves and ridges ; it is, accordingly, neces- 

 sary for the draughtsman to imagine it as artificially flattened 

 out, and the view of the dorsal aspect in particular is bound to 

 be to a considerable extent conventional or diagrammatic. 



The illustrations hitherto given by other authors are all more 

 or less inadequate. Jagerskiold's original woodcut (Zool. Anz. 

 I.e.) is very rough and gives no details : Levander's^ is in points 



1 Mr. "Western remarks to us that one can produce a similar picture to 

 Levander's by focussing too low down instead of on the suiiace of the lorica. 



