THE CRUSTACEA 



The front of the head is produced, in Anaspides, into a short 

 rostrum. On the dorsal surface, in front of the cervical groove, 

 is a pigmented area with a circular central spot surrounded by four 

 minute pits. The significance of this structure is quite unknown, 

 but it may be comparable to an obscure " dorsal organ " apparently 

 glandular in nature, occupying a similar position in certain other 

 Malacostraca. It has not been observed in Koonunga. 



The thoracic somites have no pleural plates and those of the 

 abdominal somites are slightly developed. The telson, in Anaspides 

 and Koonunga, is short, of simple form, with a fringe of spinules 

 on the posterior margin. 



Appendages. The antennules are biramous, with long flagella. 

 The first of the three segments of the peduncle contains a statocyst, 

 opening by a narrow slit on the dorsal surface. In the male 

 Anaspides the basal part of the inner flagellum is enlarged and armed 

 with serrated spines. It appears probable that it may be used as 

 a clasping-organ. In Koonunga, the antennule of the male has a 

 curious globular organ attached to the first segment of the outer 

 flagellum. The surface of the organ is covered with minute cup- 

 like structures which are possibly sensory. 



The antenna has a scale -like exopodite in Anaspides, but in 

 Koonunga this is absent. The protopodite consists of two segments, 

 and the first two segments of the endopodite are enlarged, so that 

 the peduncle consists of four segments only. 



The mandibles (Fig. 96, A) have a large palp of three segments. 

 The serrated incisor process is separated from the molar process in 

 Anaspides by a rounded lobe (s) fringed with setae. The lower lip 

 is large and deeply cleft. 



The maxillula (Fig. 96, B) has two endites and a vestigial palp. A 

 small exite, not projecting beyond the outer edge, can be recognised. 



The maxilla (Fig. 96, C) has three endites directed distally 

 and crowded together, and a short, un segmented palp. There is 

 no exopodite. 



The thoracic limbs are all alike in general structure. In 

 Anaspides (Fig. 3, E, p. 8) the endopodite Is composed of six 

 segments (instead of the usual five) in the anterior pairs, but the 

 articulation between the basipodite and ischiopodite becomes indis- 

 tinct in passing backwards along the series, and in the last three 

 pairs these segments have completely coalesced. In Anaspides the 

 main flexure of the limb is between the fifth and sixth segments, 

 but in Koonunga it appears to be between the fourth and fifth. 

 This difference, however, is due to the fact that in all the thoracic 

 legs of Koonunga, as in the posterior pairs of Anaspides, the 

 basipodite and ischiopodite have coalesced. The terminal segment 

 is small, and bears from three to five stout curved claws, one of 

 which on the posterior legs is larger than the others. 



