TEREBRATULA.—Ptate I. 
IX. Brazilian Province. X. North American Province. 
Bouchardia tulipa. Terebratulina caput-serpentis. 
DISTRIBUTION OF SUBGENERIC TYPEs. 
Terebratula.—lusitanian, Magellanic, and Panamic provinces. 
Waldheimia.—North European, North Asiatic, Indo-Pacific, Australo- 
Zealandic, and Panamic provinces. 
Terebratulina—North European, Lusitanian, North Asiatic, Indo- 
Pacific, and North American provinces. 
Terebratella—North Kuropean, North Asiatic, Indo-Pacific, Australo- 
Zealandic, and Magellanic provinces. 
Magas.—Australo-Zealandic province. 
Bouchardia.—Australo-Zealandic and Brazilian provinces. 
Megerlia.—Lusitanian province. 
Kraussia.—Austvalo-Zealandic and South African provinces. 
Morrisia.—Lnusitanian province. 
Argiope.—Lusitanian and Celtic provinces. 
Thecidea.—Lusitanian province. 
Summary. 
1. Of the thirty-nine species cited in the foregoing ana- 
lysis, thirty-five belong to the Old World, only four to 
the New. None of the species are common to both, with 
the single exception of Terebratulina caput-serpentis of the 
North European and Lusitanian provinces, which ranges 
in a modified form (7. septentrionalis, Couthouy) to the 
eastern shores of North America. Two species of Zere- 
bratula have been described by Dr. Gould in Wilkes’s ‘ Ex- 
ploring Expedition’ (7. cawrina and pulvinata), from Pu- 
get Sound, Oregon; but I have not seen them. 
2. The distribution of subgenera illustrates a few cha- 
racteristic centres of creation. Megerlia, Morrisia, Ar- 
giope, and Thecidea, all have their home in the Lusitanian 
province,—one species only, Aryiope cistellula, passing 
into the Celtic province, which has no centre of specific 
creation of its own. A7vaussia has its home in the South 
African province, embracing four species. A fifth species, 
K. Lamarkiana, is found in the Australo-Zealandic pro- 
vince; but the apophysis, on which the subgenus is founded, 
is abnormal in its structure. 
3. Of subgeneric types widely removed, Bouchardia 
presents curious instances. B. ¢udipa, a solitary species 
on the shores of Brazil, is undoubtedly identical in type 
with B. fibula and Cumingii, which are natives of Australia 
and New Zealand, though no Faunas of any two provinces 
can be more generally dissimilar. The same may be said 
of Waldheimia and Terebratella ; but these subgenera are 
more abundant in species and individuals, distributed in 
local centres of creation of more varying specific character. 
4. Of specific types widely removed, a notable instance 
is presented in Waldheimia globosa of California, and 
lenticularis, a native of New Zealand. Not only are these 
two very remote species of the same specific type, but the 
difference of their specific details is scarcely appreciable. 
5. The most characteristic assemblages of species are 
those of Terebratulina in the North Huropean and North 
Asiatic provinces, Waldheimia in the Panamic, of Zere- 
bratella in the Magellanic, and of Morrisia and Argiope 
in the Lusitanian province. 
6. Species are fewest within the Tropics. The Indo- 
Pacific province, which extends from Australia to Japan, 
and from the Red Sea and east coast of Africa to Haster 
Island in the Pacific, embracing three-fifths of the circum- 
ference of the globe and forty-five degrees of latitude, 
yields only three species—Waldheimia picta, Terebratulina 
Cumingi, and Terebratella sanguinea ; and of the first two, 
very few individuals are known. 
7. Species, with few exceptions, are very local. The 
exceptions are Terebratulina caput-serpentis, which ranges, 
as already noticed, from the Arctic to the Mediterranean 
Seas and to the seas of North America, and is very closely 
represented in the North Asiatic provinces by 7. Japonica 
and abyssicola. Another exception to the local distribution 
of species is presented in Waldheima picta, which is found 
both at Java and at the Friendly Islands. A third excep- 
tion is one of similar character: Terebratella sanguinea 
inhabits both the Philippine and Sandwich Islands. And 
a fourth exception occurs in Zerebratula wva, collected 
originally at Guatemala, but of which small specimens, in 
the British Museum and in Mr. Cuming’s collections, have 
been received from the Falkland Islands. 
8. Lastly, the Australo-Zealandic province may be no- 
ticed as being the most prolific of forms and brilliancy 
of colour; but all the subgenera of this province, with 
the exception of Mayas, have species, though none of the 
same, in other provinces. 
The Zerebratule live at various depths, reaching nearly 
to the deepest limit of molluscan life, attached to corals, 
stones, fragments of shells, and to one another. The na- 
tural position of the animal is to repose upon its back, 
the smaller or dorsal valve being undermost, and a mooring 
is secured by means of the byssus-like tendon or pedicle 
let down from the overhanging ventral valve, which is 
beaked on one side and perforated for the purpose. The 
perforation is very liable to erosion and damage from the 
buffeting of the water, more so in some species than in 
others, and it becomes more or less enlarged accordingly. 
To meet this the area below the perforation is constructed 
of a pair of plates, termed the deltidium, and as the 
foramen enlarges, the plates separate from each other like 
a sliding panel. The substance of the shell is invariably 
punctured throughout, differing generically in this respect 
from that of Rhynchonella, and it is a beautiful object under 
the microscopic, or even under an ordinary lens. 
For description of the accompanying plate see Pl. II. 
