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 scaflfolding 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. 



Rhymhomlla 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 Terehrahdina the brachial skeleton forms a simple loop ; in 

 Magellania the loop is reflected on itself (Fig. 2). 



The beautiful and unique specimen of DyscoUa ivyvillii, from 

 390 fathoms W. Indies, is remarkable for its size, being over two 

 inches in length. The small vitreous specimens of Terebratula 

 ivyvillii 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. 



