146 HALOMENIA GRAVIDA. 



structure in Proneomenia hawaiiensis for example, and is apparently not inner- 

 vated by a well-defined subradular nervous system. 



The oesophagus opens at the summit of a papilla (Plate 11, fig. 3) into the 

 stomach-intestine, which manifests no especially noteworthy features save that 

 its lining is of such thickness that in preserved material it reduces the cavity to 

 a narrow slit. In the posterior end of the body the gut narrows to a vertical 

 slit as it passes between the anterior ends of the shell gland then becomes a 

 circular canal of small size that opens into the cloacal cavity dorsal to the external 

 reproductive opening. 



The circulatory system is almost the exact counterpart of that in A. 

 agassizi. 



The reproductive system is likewise practically identical with that of the 

 foregoing species. The pericardial cavity is .smaller, and the inner ends of the 

 coelomoducts are more slender, but they rapidly increase in size and their walls 

 become more than usually folded. The shell gland, especially its posterior half, 

 is more distinctly lobulate and somewhat more acid in reaction. The seminal 

 receptacles are considerably larger; but neglecting these differences the two 

 species agree closely so far as this system is concerned. 



The nervous system is not especially favorable for study and for this reason 

 only the more obvious portions have been examined. In all essential particulars 

 these closely resemble homologous structures in the foregoing species. 



Halomenia gravida, sp. no v. 



This species is represented by two individuals taken off Simushir Island 

 of the Kurile group at a depth of 229 fathoms (Sta. 4804). Both were discovered 

 in dead barnacle shells and are evidently free roving forms. The larger speci- 

 men is 11 mm. long by 1.6 mm. average diameter and the length index 7:1 

 is characteristic also of the smaller one. The anterior cirrose section of the gut, 

 or the atrium, is separated from the succeeding portion by a ridge (Plate 5, fig. 3) 

 covered with the spiculose cuticle investing the body. Posteriorly the pedal 

 groove is continuous with the cloaca which like the atrial opening, extends far up 

 toward the dorsal surface of the body. The color is light yellow shading to 

 nearly white in the head and cloacal regions (owing to compact muscles) and 

 along the mid dorsal line where the gonad is situated. A dorsal sense organ is 

 present (Plate 22, fig. 12), and is remarkable for its large size and from the fact 

 that it is more anteriorly located than is usually the case with other species, 

 being placed opposite the forward cloacal wall. 



