TEREBRATULID^. 311 



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 at 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 longitudinall}'^ 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. T. 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 becomes very diminutive in some species, and is obsolete in 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. Gumingii. 



WALTONiA, Davidson, 1850. Shell with the beak truncated by 

 a large incomplete foramen ; deltidia separate. Loop reduced 

 to two simple lamellae furnished with oral processes and attached 

 to a prominent central septum. T. Valenciennesii^ Davidson. 

 Perhaps the fry of Ter. rubicunda, with the reflected part of 

 the loop wanting. 



TRiGONOSEMUS, Kouig, 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. 5 sp. Chalk; Europe. T. eZeyans, Kcinig (cxxxv, 30-32). 

 T. Falissii, 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. T. lyra^ Sowb. (cxxxv, 34, 

 35). T. neocowiensis, d'Orb. (cxxxv, 36). 



MEQERLiA 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. 37-39). 



LAQUEUS, Dall, 1870. Shell with the reflected portion of the 

 loop attached by slender processes, on each side, to the haemal 

 processes, at or near the points where the two septal processes 



