82 SHELL GALLEKY. 
Order 4. Telotremata. — This group, which at the present day- 
contains the largest number of species, includes the Lamp shells, 
so called from their resemblance to an ancient lamp. The valves 
are joined by a well-marked hinge, the peduncle passes through the 
peduncle valve through a foramen completed by two plates secreted 
by the mantle edges, and the brachial valve has attached to it a 
calcareous scaffolding of processes or loops for the support of the 
" arms." 
The shells in this group are frequently ridged. Their colour 
is usually white, but sometimes red or yellow ; deep-sea forms are 
generally vitreous. 
Rhynchonella psittacea has a black shell with a pointed incurved 
beak ; each of the arms forms a many coiled spiral and can be pro- 
truded beyond the shell ; the brachial skeleton is comparatively small 
and simple, consisting of two separate processes. 
In Terebratulina the brachial skeleton forms a simple loop ; in 
Mag ell an ia the loop is reflected on itself (Fig. 2). 
The beautiful and unique specimen of Dyscolia ivyvillii, from 
390 fathoms W. Indies, is remarkable for its size, being over two 
inches in length. The small vitreous specimens of Terebratula 
ivyvillU were obtained off Chili from a depth of 2160 fathoms ; 
specimens of the same species were obtained also from a depth of 
2900 fathoms in the North Pacific. 
