} } 



284 Memoirs of the Indian Museum. [Vol. I, 



shield are long and spike-like (pi. xxi, fig. 3),. projecting outward, while on the sur- 

 face of the shield they converge on the aperture which occupies the centre. 



This aperture leads into a spherical cavity which contains a gill (pi. xxi, fig. 4). 

 This latter organ consists of an oval mass divided into two bilaterally symmetrical 

 halves, each built up of lamellae which lie in the transverse plane of the animal. 

 The gill of course recalls the caudal branchiae of Priapulus. In Priapulus, however, 

 the structure lies ventral to the anus, while in Investigator it is dorsal to it. 



The anus curiously enough opens into this respiratory chamber on its ventral sur- 

 face not far from the external opening. 



In regard to colour, the head of the animal is pink, the body and neck olive- 

 green with an added silvery sheen caused by the spines. 



Measure^ments. 



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



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



Neck length . . . . . . . . 18 — 19 



Head .... . . . . 4 



These measurements are from preserved specimens. 



Skin and body-wai,i,. (PI. xxi, fig. 5.) 



The ectoderm is represented by a protoplasmic layer which does not show cell 

 outlines. Nuclei are scattered freely throughout it. The spicules and spines give the 

 appearance of having been simply thrust into this layer. A few nuclei are aggre- 

 gated around their bases, but there is no definite formative sheath. 



Under the ectoderm a thin layer of circular muscular fibres is to be found 

 throughout the entire length, and in the neck in addition to this a layer of longitudi- 

 nal muscles occurs divided into four bands — two dorsal and two ventral. 



The head corresponds physiologically to the ''introvert" of other Gephyreans. 

 The skin is smooth, and numerous bundles of muscle fibres arising from the wall of 

 the pharynx and anterior portion of foregut are inserted on its cœlomic surface and 

 can doubtless easily introvert this portion of the body, although none of the speci- 

 mens before me show this condition. 



The retractor muscles receive an extraordinarily rich nerve supply from the two 

 lateral nerve cords. Ivarge nerves run out to them and in several places form ganglia 

 among the interlacing muscle fibres. 



The body-cavity. 



The body-cavity extends continuously from the head to the shield, surrounding 

 the alimentary canal. The liver, nephridia, gonads and splanchnic blood-vessels also 

 lie within it. 



The space is apparently completely lined by endothelium, a parietal layer on the 

 body- wall, a visceral layer covering the organs above mentioned. This endothelium 



