148 



but it does not extend to the margin of the shell, and there is 

 generally a more or less deep pit on the ioner surface, in front of 

 its extremity. 



"Wheu I first saw ttie shell, I was inclined to regard it as a mon- 

 strosity ; but ^vhen I considered the uuiformity of the peculiarity 

 in the specimens which I possess, and in those which Mr. Cuming 

 had seen, I thought that it might be the type of a new form, for 

 which Schismotis excisa would be a good name. 



But a comparison of the shell with the specimens of Haliotis al- 

 bicans in the British Museum from Van Diemen's Land, has induced 

 me to believe that they are only varieties of that or some very nearly 

 allied species, and that the peculiarity of their structure is produced 

 by the locality they inhabit, the absence of the shelly matter on the 

 branchial ridge being probably produced by the continued abrasions 

 to which the shells have evidently been exposed, either by some che- 

 mical peculiarities in the water or the attack of parasitic animals. 



Ali the specimens are in a very eroded condition, and two of them 

 are very much pierced with a minute vrorm, and they all have the 

 under valve of a Hipponyx attached on the left side near the circum- 

 ference of the shell ; one of these shells (which is generally the 

 largest of the series) beuig placed in front of the sht between its 

 termination and the front margin of the shell, covering the space 

 which in the normai shell would be the place of one or two perfora- 

 tions. 



If the exterior surface of a good specimen of Haliotis albicans is 

 examined, it will be found that there exists a distinct narrow straight 

 groove continued from one perforation to the other, and to the margins 

 of the outer lip, which I have not seen so distinctly marked in any 

 other species of the genus, indicating probably the suture betvveen 

 the overlapping of the two sides of the slit in the mantle of the animal, 

 and this suture is marked but by a slight line on the inner surface 

 of the shell. The šame suture is to be observed in most other 

 Haliotidce, but they are generally not so distinct as m H. albicans, 

 and much more sinuous. 



I am inclined to beheve that the slit in the specimens is to be 

 considered as the imperfect filling-up of the shelly matter between 

 the usual perforations, caused by the eroded and evidently diseased 

 State of the specimens. 



The interior of the shells is marked with a very rough tubercular 

 muscular scar, which is not to be observed in perfect specimens oi Ha- 

 liotis albicans ; but this will be found to be uniformly the case with 

 most specimens of Ear-shells which have an eroded or worm-eaten 

 outer surface, even in species which have a scarcely marked scar in 

 their perfect or normai condition ; so that this difference, likę the 

 slit, appears to depend on the statė of the shells and the animal 

 which formed it. 



The interior of the shell presents a further peculiarity, but this is 

 evidently caused by the šame effects as the roughness of the muscu- 

 lar scar and slit on the branchial ridge, viz. there is a more or less 

 deep broad groove on the inner surface between the slit and the sub- 



