REPORT ON THE GASTEROPODA. 



31 



are regular, delicate, well rounded, raised and unequal, a few being a little stronger than 

 the rest, which, to the number of two to four, closely occupy the intervals. Spirals — these 

 are microscopic, rounded, close-set, and very faint. Colour : under the strongish, hard, mem- 

 branaceous, pale brownish epidermis the shell is porcellanous white. Apex : the embryo- 

 nic apex has been removed, and a scarred plug at the very top of the back slope fills the 

 hole it left. Margin thin and broken, and overlapped by the epidermis. Inside por- 

 cellanous, delicately fluted, open to the apex, with a strongish horse-shoe scar, with two 

 oval muscular impressions, and the prominent head-scar shaped like that in Patella, only 

 somewhat larger in proportion. L. 0"13 in. B. 0"07. H. 0'07. 



I dissected the animal of this species with great care, but not much satisfaction, the specimen 

 being extremely small and necessarily somewhat damaged by preservation in spirit. No eyes could 

 be seen ; but as their absence on the surface is sometimes due to a power of internal withdrawal, I 

 looked for them carefully during dissection, but in vain. There were no appendages to the side of 

 the foot or on the mantle-edge, a feature on which Mr Dall dwells in establishing the genus. He 

 describes the branchia as a single asymmetrical gill, but plumose. In the Challenger species 

 there was no appearance of a plume, but a somewhat stumpy finger-shaped process projected back- 

 ward from the lower right side of the neck ; and from the side of this process another, very 

 much smaller, issued in the same direction. The surface of both these (and of them alone) was 

 finely tessellated or beaded ; and in each bead there seemed to be the loop of a blood-vessel. The 

 dentition is, as Mr Dall observes, very like that of Scutus australis, Quoy, given in Gray's Guide, 

 p. 163, so far, that is, as general arrangement and relation are concerned ; but in Cocculina angulata the 

 centre tooth is higher and narrower, with a much smaller cusped point, and is shouldered at either 

 side ; the three following laterals on either side in form and position are like those given by Gray at 

 p. 190 (not p. 172), fig. 103, as those of Lepeta cceca, only that the inmost one has three, the second 

 two, and the third one cusp. Thus far, therefore, Gray's figure of Lepeta earn, p. 1 90, agrees better, 

 so far as it goes, with the toothing of Cocculina angulata ; but beyond the three small laterals occurs 

 a single largish bicuspid tooth, not nearly so formidable a weapon as that of Scutus australis, whicli 

 is enormously larger, more curved, and tricuspid. Beyond these, as in Gray's figure, but very 

 much more numerous and more crowded, are an infinity of small hooked laterals. Attaching very 

 little value to systems of classification of Mollusca based on dentition, I should have hesitated to 

 follow Mr Dall in separating this group from Lepeta ; but there is one fact which probably is a suffi- 

 cient reason for a step otherwise much to be deplored, viz., that in Cocculina the long slope of the 

 shell is in front, a feature which the genus shares with PropUidium in common with the whole of 

 the " Fissured Limpets," and which contradicts the common rule for the unfissured Limpets, that the 

 short slope is in front. 



Dentition of Cocculina angulata, Wat?., highly magnified. 



