582 Transactions. 



Art. LI. — Anatomij of Siphonaria obliquata (Sniverhy). 



By A. J. CoTTRELL, M.A., M.Sc. (N.Z.).* 



Communicated by Professor Benham. 



[Bead before the Otago Institute, 1st November, 1910.] 



Plates XXVIII, XXIX. 



Habits, etc. 



Siphonaria ohliquata is a marine Gastropod, being one of the commonest 

 characteristic of our shores. Superficially it resembles the limpet, and, 

 like the latter, it is found in rocky places attached to rocks which are 

 covered at high tide. I have collected specimens of this mollusc on the 

 rocky beaches at Portobello (Otago Harbour), St. Clair, Brighton (Dunedin), 

 and Oamaru. I have also examined specimens collected at Kaikoura, and 

 also some very fin*^ specimens from Wellington. When out collecting I 

 have found them always in the same regions as limpets, but on the parts 

 of the coast I have visited they are not nearly so plentiful as the latter. 

 As a rule, the large specimens were found in out-of-the-way crevices in 

 the rocks, well above the low-water mark. Others, however, were found 

 nearer the low- tide mark, while many of the smaller specimens were col- 

 lected from pools. 



Externals. 



The Shell Plate XXVIII, figs. 1, 4, 5 ; Plate XXIX, fig. 1. 



The mollusc is protected by a strong calcareous conical shell, which 

 can easily be distinguished from that of the limpet by the following fea- 

 tures : — 



In Siphonaria the apex of the shell lies nearer to the posterior end and 

 to the left side of the middle line, while in Patella (all species found on our 

 coast) the apex lies nearer the anterior end of the shell, and in the middle 

 line (Plate XXVIII, figs. 1, 4, 5; a). 



Ridges radiate from the apex to the margin, which is notched, and 

 concentrically are the lines of growth. On the right side, starting from the 

 apex and extending to the edge of the shell, is a triangular ridge which 

 corresponds on the inner side of the shell to the siphonal groove or notch 

 (Plate XXVIII, figs. 1, 5 ; Plate XXIX. fig. 1 ; sh). The external surface of 

 the shell is dark in colour, resembling the rocks to which the creature adheres, 

 while the inner surface is of a light colour, varying from a light cream to 

 a brownish-yellow. The interior of the shell is coated with the usual 

 nacreous layer, in which the muscle-impressions can be seen (Plate XXIX, 

 fig. 1 ; mt). These indicate the points of attachment of the pallial muscli's, 

 both past and present. They form an almost complete ring, broken only 

 in the region of the siphonal notch. 



Bodii-waU. Plate XXVIII, figs. 1, 4. 

 The creature is divisible into head and body, but there is no neck. 

 During locomotion these parts are distended, and protrude considerably be- 

 yond the shell (Plate XXVIII, figs. 1, 4), but when the tide is out the body 

 is drawn into the shell, which comes into close contact round its margin 



* This article is part of the thesis upon whicli the University of New Zealand 

 awarded the author first-class honours in 1006. 



