RISSOA. 365 
R. puncrursa, Montagu. 
R. punctura, Brit. Moll. iii. p. 89, pl. 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 im 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 im 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 beng 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. sotura ? Philippi. 
R. soluta, Brit. Moll. i. p. 131, pl. 75. f. 3, 4, and iv. p. 265, 
The animal occupies a simple, elegant, minute, spirally 
