Deep-water Limpets and Chitons. 23 
It is likely, however, that Scutellina, when investigated, will 
prove to have very similar dentition *. 
Chitonide. 
Genus CHZTOPLEURA (Shuttleworth), Cpr. 
Chetopleura apiculata, Say. 
Habitat. Station 938, United-States Fish Commission, 
1881, being 100 miles 8.E. by E. 3 E. (magnetic) from Gay- 
Head Light, Martha’s Vineyard. 'The depth was 210 fathoms, 
green sand and mud, the bottom-temperature 40°°5, the sur- 
face 72°-0 F. 
In these researches only two specimens of Chitonide were 
obtained; and these are not of a genus characteristic of the 
deeps. ‘These specimens were young, but did not differ from 
young ones of the same species from shallow water. There 
have been found in depths of 100 fathoms or less along the 
north-eastern coast of New England, and northward, two 
other tolerably common Chitons, one of them, Trachydermon 
albus, Linné, which does not go to great depths, as far as 
known, either in the Atlantic or Pacific. In Alaska it is 
abundant from low-water to 100 fathoms. The other, Lepto- 
chiton cancellatus, Sowerby, occurs off the British possessions, 
and may reach a depth of 300 fathoms. Rarer species, which 
may be found in deep water are :—Leptochiton alveolus, Sars 
(150 fathoms, Gulf of Maine) ; Hanleyia mendicaria, Mighels 
and Adams; H. debilis, Gray (to 300 fathoms) ; and H. tro- 
ptcalis, Dall, from southern waters (Sand Key, 128 fathoms). 
The greatest depth from which Chitons have been reported 
is 1006 fathoms, at which the Leptochiton Belknapt, Dall, 
was obtained in the North Pacific. It has since turned up 
from Kerguelen in the ‘ Challenger’ collections, and, perhaps, 
may eventually be found in the North Atlantic. 
Notes on the Genera. 
The slender side teeth of Lepeta are distinguished from 
true laterals by not being situated on the central longitudinal 
area of the radula. By their form alone it would be impos- 
sible to distinguish them from teeth which are truly laterals, 
like the inner laterals of Lepetella. 
Since 1869 (when I revised the classification of the Lepe- 
tide, and, somewhat later, of the order to which they belong) 
* I should be most thankful for a dried or alcoholic specimen of 
soft parts of the typical species of Scwtellina (S. crenulata, Broderip). 
