9 o 



Memoirs of the Indian Museum. 



[Voi,. V, 



Fig. 6. — Halianthus limnicola, sp. nov. 



Transverse section of the column in the middle of 

 the stomodaeum. 



The circular muscle of the body-wall is well developed and in the living animal 

 can be detected readily with the aid of a hand-lens as a series of transverse rings 



capable of independent contraction and 

 expansion. The differentiation is, how- 

 ever, physiological rather than anato- 

 mical and in vertical sections the muscle 

 forms a continuous sheath of minute 

 fibres, having the general appearance of 

 an irregularly serrated line more conspi- 

 cuously folded at some points than at 

 others. In transverse sections the fibres 

 lie at the base of the endoderm (as of 

 course they do also in vertical sections) 

 but run across the mesogloea at the 

 base of the mesenteries. The muscular 

 sheath is most strongly developed in 

 the wall of the physa. 



The sphincter (pi. vii, fig. 4) is well 

 developed but short. It lies close below 

 the base of the tentacles and consists of 

 a number of relatively stout isolated 

 strands surrounding distinct muscle-spaces and well separated by mesogloea from the 

 muscle-sheath. 



The stomodaeum is spacious in cross-section ; the walls, which are moderately 

 thick, are thrown internally into three distinct though not very deep folds on either 

 side; the sulcus and sulculus are very broad. The sulco-sulcular length in a state 

 of expansion occupies a little less than a half of the width of the column. 



There are no rudimentary or incomplete mesenteries. The twelve complete 

 mesenteries are normally fertile. The kidney-shaped muscle-banners are moderately 

 small and separated by some little distance from the wall of the stomodaeum ; they 

 contain a considerable number of moderately long and slender folds of the mesogloea. 

 The parietal muscles are slightly and irregularly folded, the projections of the 

 mesogloea on which they are based being by no means clearly defined in sections. 



The gonads are normal in structure and not very much folded transversely. 

 The animal appears to be dioecious. 



The specific characters of Halianthus limnicola may, therefore, be summarized as 

 follows : — 



(1) The whole animal (except the internal organs) is colourless and translucent 



or hyaline, the markings on the tentacles being due to relative degrees 

 of transparency and not to pigmentation. 



(2) The normal shape of the column is conical and there is no external differ- 



entiation of capitulum, scaphus and physa. 



(3) There is no external sheath or cuticle. 



