THE EXOGONE.-E. 225 



The length of a mature specimen is, on the average, about 5 mm. with a 

 breadth of about "5 mm. The number of segments varies from about 25 to 

 over 40. The length of the segments is approximately half the breadth. 

 The colour is grey or reddish- or yellowish-grey, and is regulated by the 

 amount of adherent debris. The colour, when present, is due to diffused 

 irregular dots of red pigment. 



The palpi, which equal prostomium and peristomium in length, are, as in 

 other species of the genus, closely united together, separated by a median 

 groove and a terminal notch. The distal part is contracted, the narrowing 

 usually taking place rather abruptly ; the narrower terminal part is often 

 bent sharply downwards so that it becomes invisible when the animal is 

 looked at from above. Mftst specimens have the palpi entirely devoid of 

 papillae, but in a few cases two symmetrically placed pairs of very distinct 

 papillae are present on the dorsal surface of these appendages. The tentacles 

 are of equal length, scarcely extending as far as the distal end of the palpi. 

 The basal portion of each is dilated, the distal narrow — the dilated and narrow 

 parts being of nearly equal length. Under some conditions, or in some 

 individuals, the dilated parts of the tentacles (and the same holds good of 

 the cirri) become almost spherical and the narrow terminal parts greatly 

 reduced. There are never more than four eyes, the " frontal ,J> pair present 

 in some nearly-related species being absent. The size of the eyes varies 

 greatly, being greatest in individuals with ripe sexual products. The single 

 pair of peristomial tentacles are similar to the prostomial. 



The dorsal surface of the peristomium and the segments of the body are 

 ornamented with papilla?. The surface of the body is very usually covered 

 with a layer of granular debris adhering to the surface, and this may com- 

 pletely hide the papillae, but, when the latter are distinguishable, their 

 arrangement is extremely regular, about fifteen pairs being symmetrically 

 placed on each segment. On the ventral side also papillae are present, but 

 these are smaller and less numerous than those of the dorsal surface. 



The dorsal cirri closely resemble the tentacles in form and size. They are 

 about equal in length to the corresponding parapodia, but may project beyond 

 them. They bear each a small number of papillae, but, these are never so 

 prominent as those on the body and parapodia and are sometimes very 

 obscure. The dorsal cirri of the second setigerous segment were absent in 

 all the specimens examined for them. 



The ventral cirri are smaller than the dorsal, and not definitely dilated at 

 the base. The anal cirri do not differ notably from the largest of the dorsal 

 cirri and resemble them with regard to the papillae. There is no posterior 

 median process, but three pairs of papilla?, rather larger than those on the 

 General surface, lie between (he anal cirri. 



The parapodia (PI. 18. fig. 33) are in length about half the breadth of the 

 body, of compressed conical shape. Each bears two prominent papillro 

 towards its extremity. The single aciculum has its terminal part bent 



