RISSOA. 365 



R. PUNCTURA, Montagu. 

 R. punctura, Brit. Moll. iii. p. 89, pi. 80. f. 8, 9. 



This species has been confounded with the preceding, but 

 having met with many live specimens, it will be seen that 

 Montagu has properly distinguished it. The animal is lively 

 and freely shows its organs, and in this instance I have it in 

 my power to effect a description by reference. It is in every 

 respect identical with the R. reticulata, with the exception of 

 a particular-seated and constant variation of colour; the oper- 

 culigerous lobe is a very pale muddy reddish-brown, but it is 

 marked on each side, close to the junction of the foot with 

 the body, with an irregular, rather large, dark, smoke-coloured 

 stripe, which is invariably wanting in R. reticulata. 



Though differences of colour are not generally to be 

 received as good specific characters, yet, when we see certain 

 markings in an animal in a particular position, which are 

 always absent in one that resembles it in almost every other 

 point, we are entitled to consider them as fair specific dif- 

 ferences ; and in this case distinctness is corroborated by a 

 considerable variation in the contour of the two shells, the 

 R. punctura being much smaller, with more rounded and less 

 tumid volutions, as well as having the sutures more deeply 

 impressed than in the R. reticulata. 



Since the above observations were made, I have taken many 

 of this and the preceding species, and in the present animal 

 have always found the dark lead-coloured marks on the opercu- 

 ligerous lobe, with the addition under the neck, near the eyes, 

 of a small red dot; but these particulars are absent in the 

 R. reticulata, the same parts being pure white. Both inhabit 

 the coralline zone, and at Exmouth the R. reticulata is strictly 

 confined to a coralline area, whilst the R. punctura occupies 

 the interstitial grounds of that district, in muddy patches, 

 mixed with comminuted shelly spoil. I cannot doubt the 

 distinctness of the two. 



R. SOLUTA ? Philippi. 



R. soluta, Brit. Moll. iii. p. 131, pi. 75. f. 3, 4, and iv. p. 265. 

 The animal occupies a simple, elegant, minute, spirally 



