on the Chitonide. 29 
zona tomentosa obyelata, omnino tecta. Zona (in utroque scuto) fissura 
porisque duobus tubulosis lateralibus signata: supra scutum anticum 
poriquatuor. Branchie abbreviate. 
Ex. Ch. porosus, Burrow. 
Has divisiones subgenericas non omnes egomet vidi, at lubenter recepi. 
Squame et sculptura semper oculis armatis examinande. 
These animals frequent the rocks and stones of the sea-coast, and are 
distributed nearly over the whole globe. Many of the species are con- 
stantly under water, while others ascend above low or even high water- 
mark, spending the day exposed to the hottest sun, or selecting a rest- 
ing-place which is only occasionally moistened by the rude and restless 
surf, In Chitonellus and Cryptoconchus there are certain minute organs 
on the zone, which bear a strong resemblance to the spiracula of the 
annulose animals. From their habit of quitting the watery element, like 
many of the Turbinide, I once supposed that the organs for the aeration 
of the circulating fluid might be of a compound nature, (pulmono-bran- 
chiati.) It is, however, far more probable (as in the case of some Crus- 
taceous* genera which I am now investigating,) that this process is capa- 
ble of a diurnal or a temporary interruption, or that the branchie, so 
long as they are kept moist, and shielded from atmospheric influence, 
may perform their functions, though much more slowly. 
The species are very numerous, but involved in the greatest confusion. 
As De Blainville has remarked, ‘* Leur séparation en petits groupes na- 
** turels est assez difficile, nous ne doutons cependant pas qu’on y paryi- 
** enne, si l’on peut réussir a étudier a la fois et compiétement les ani- 
«* maux et les coquilles.” From the great variation in their colouring, 
and the liability of the older shells to become corroded and decorticated 
by atmospheric exposure, the action of salt water, or the blows of roll- 
ing stones, while the spines and other appendages of the zone, are worn 
* In the decapod short-tailed Crustacea which reside at the bottom of the 
ocean, the foramina which admit the water to the branchie are very large: in 
the genera which dwell long on land they are contracted. These curious open- 
ings, seated at the base of the arms, and closed with a moveable operculiform 
ciliated janua, 1 have termed portule. 
