içog.] F. H. Stewart : Investigator sicarius. 29Î 



Genus Investigator, gen. nov. 



It seems prudent to leave the definition of the genus until the discovery of other 

 species and to proceed without further delay to the definition of — 



Investigator sicarius, sp. nov. 



Body divided into trunk, neck and head. Trunk sausage-shaped, narrowing 

 fairly abruptly to the neck which is approximately one-and-a-half times the length 

 of the trunk. Head globular, introvertible. No tentacles. Mouth slit-like, situated 

 on a diamond-shaped area of specialized skin. Posterior to this area the head bears 

 several circles of simple spicules. The skin of the neck and trunk is imiformly 

 covered with glassy chitinous spines, needle-shaped on the anterior portion of the 

 neck, broadly lanceolate on the trunk. The hind end of the body is formed by a 

 flatly conical shield. The spines at the edge of the shield are long and spike-like, 

 projecting outward, on the surface of the shield they converge on an aperture in the 

 centre. This aperture leads into a gill-chamber containing a bilaterally divided gill. 

 The anus opens on the ventral wall of this chamber. Nephridia two, opening at 

 the edge of the shield. 



Colour. — Head pink, neck and trunk olive-green with a silvery sheen due to the 

 spines. 



Measurements. 

 Trunk length . . . . . . . . 12 — 13 mm. 



,, max. diameter . . . . . . 5 ,, 



Neck length .. .. .. ,. 18 — 19 ,, 



Head „ .. .. .. .. 4 ,, 



Habitat. — Bay of Bengal and Indian Ocean, at a depth of 250 — 600 fathoms, on 

 a muddy bottom. 



Some considerations of Comparative Morphoi^ogy. 



I. Relationship of the post-anal region of Investigator to the similar region of 

 PriapulidcB. By the post-anal region in Investigator is to be understood that portion 

 of the respiratory chamber lying in front of the anus, and the gill. The respiratory 

 chamber from its opening to the base of the gill-stalk is formed by an invagination of 

 the body-wall and thus clearly all that lies actually in front of the anus is morpholo- 

 gically posterior to it. Now if in imagination this chamber be again everted so that 

 it projects behind the anus as a conical tail with the gill at the tip, we get a structure 

 bearing a very striking resemblance to the post-anal region of Priapulids. It is hol- 

 low, the cavity continuous with the cœlom. On its surface are projections of respira- 

 tory lamellae. The gill is merely an exaggerated respiratory papilla. So far the 

 resemblance is very striking, but, as has been pointed out above, the post-anal region 

 of Investigator lies dorsal to the anus, that of the Priapulidce ventral to it. 



