CLASS II BRACHIOPODA 303 
margin of the ventral valve. In derived forms this is progressively closed posteriorly ; 
geologically in the phylum, and ontogenetically in the latest derived individuals. 
Habitat and Distribution.—Brachiopods are usually gregarious in 
habit, often growing in clusters attached to one another. This is not only 
true of recent species, but of Palaeozoic forms as well. Brachiopods are found 
in all latitudes and at all depths, occurring most abundantly between tides 
and 278 fathoms. Liothyrina Wyvillii was dredged from the enormous depth 
of 2945 fathoms. Terebratulina caput-serpentis ranges from a few fathoms to 
a depth of 1195 fathoms. 
Brachiopods are most prolific in warmer seas, the Japanese province having 
nearly thirty species. As a rule, those occurring in cold waters are not found 
in warm waters. Oehlert has shown, however, that a few species are world- 
wide in their distribution (Liothyrina vitrea, var. minor and Terebratulina caput- 
serpentis), and that they also have great bathymetric range. Some generally 
distributed Palaeozoic species are Atrypa reticularis, Leptaena rhomboidalis, and 
Productus semireticulatus, 
Migration of Brachiopods is possible only during the early larval stages, 
and then to a very limited extent. Morse observed that Terebratulina became 
attached in a few days, but Miiller kept Déscinisca in confinement nearly a 
month before any became sessile. Deep-sea Brachiopods are usually thin- 
shelled, brittle, and translucent. 
Colour.—‘ The shells of most living species are of light or neutral tints, 
white or horn-colour. A deep orange-red in radiating bands or in solid tints, 
colours some species (Terebratulina, Kraussina, ete.) ; light yellows, deep and 
light shades of green (Lingula), black in bands (Crania), or masses (Rhynchonella) 
embellish these shells. Even among the fossil species traces of faded colour- 
marks are occasionally observed ; Deslongchamps has described them among 
Jurassic species, Davidson among the Carboniferous, and Kayser has found a 
colour-marked Fhynchonella in the Devonian. The large highly ornamented 
species of Palaeozoic times, with their external sculpture heightened by a 
brilliant colouring, must have been objects of exquisite beauty” (Hall and 
Clarke). 
Classification.—The Brachiopoda, since 1858, have been divided by 
nearly all systematists into two orders, based on the presence or absence of 
articulating processes. These divisions, ‘“ Articulés and Libres,” were recog- 
nised by Deshayes as early as 1835, but not until twenty-three years later 
were the names Lyopomata and Arthropomata given them by Owen. These 
terms have been generally adopted by writers, though some prefer Jnarticulata 
and Articulata, Huxley, or Bronn’s Heardines and Testicardines. Bronn (1862) 
and King (1873), while retaining these divisions, considered the presence or 
absence of an anal opening more important than articulating processes, and 
accordingly proposed the terms Plewropygia and Apygia, and T'retenterata and 
Clistenterata respectively. In many Palaeozoic rostrate genera of Clistenterata, 
it has been shown that an anal opening was also present, and therefore the 
absence or presence of this organ is not of ordinal value. 
The first attempt to construct a classification of the Brachiopods was that 
of Leopold von Buch, who took for his principal differential characters the 
conformation of the umbonal region, the presence or absence of a pedicle, the 
nature of the deltidium, and the external form and ornamentation of the shell. 
