TEREBRATULIDA. al 
the slender crura proceed, first in a direct line, and then one 
division of each, diverging into the centre of the ventral valve, 
terminate in acute points. On the other side the divisions 
extend nearly «t right-angles to the axis of the shell into the 
cavity of the dorsal valve; and thence bending abruptly forward 
and gradually converging, terminate above the centre of the 
shell in a thin flattened or longitudinally concave plate. 
TEREBRATELLA, d’Orbigny, 1847. 
Syn.—Delthyris, Menke, 1830. Ismenia, King, 1850. 
Distr.—Excluding subgenera, 12 sp. Cape Horn, Valparaiso 
(ninety fathoms), New Zealand, Japan, California, Ochotsk, 
Spitzbergen, Labrador. Fossil, 16 sp. Lias—; United States, 
Europe. 7’. Magellanica, Chemn. (cxxxv, 28, 29). 
Shell smooth or radiately plaited ; dorsal valve longitudinally 
impressed ; hinge-line straight, or not much curved; beak with 
a flattened area on each side of the deltidium ; foramen large ; 
deltidium incomplete; loop attached to the septum. 
Animal like Terebratula; the spiral lobe of the brachial disk 
becomes very diminutive in some species, and is obsolete in 
T. Cumingit. 
WALTONIA, Davidson, 1850. Shell with the beak truncated by 
a large incomplete foramen; deltidia separate. Loop reduced 
to two simple lamelle furnished with oral processes and attached 
to a prominent central septum. TZ. Valenciennesii, Davidson. 
Perhaps the fry of Ter. rubicunda, with the reflected part of 
the loop wanting. 
TRIGONOSEMUS, Konig, 1825. (Delthyridea, King, 1850. Fissi- 
rostra, d’Orbigny, 1847.) Shell finely plaited, beak prominent, 
curved, with a narrow apical foramen; cardinal area large, 
triangular; deltidium solid, flat; cardinal process very promi- 
nent. 5sp. Chalk; Europe. 7’. elegans, Kinig (cxxxv, 30-32). 
T. Palissit, Wood (cxxxv, 33). 
LYRA, Cumberland, 1816. (Terebrirostra, d’Orb, 1847.) Shell 
ornamented with rounded ribs; beak very long, divided length- 
wise internally by the dental plates; loop doubly attached? 4 
sp. Cretaceous; Europe. Three species of similar form are 
found in the Trias of St. Cassian. TZ’. lyra, Sowb. (cxxxv, 34, 
35). T. neocomiensis, d’Orb. (exxxv, 36). 
MEGERLIA King, 1850. (Muhlfeldtia, Bayle, 1880.) Loop 
trebly attached; to the hinge-plate by its crura, and to the 
septum by processes from the diverging and reflected portions 
of the loop. 3 sp. Mediterranean, Philippines. Fossil, 7 sp. 
Chalk—. T. truncata, Lam. (cxxxv. 37-389). 
LAQuEvs, Dall, 1870. Shell with the reflected portion of the 
loop attached by slender processes, on each side, to the hemal 
processes, at or near the points where the two septal processes 
