256 ARCIDA. 
Shell thick, subrhomboidal, beaks anterior; hinge with a few 
oblique anterior teeth, and one or more long, laminar posterior 
teeth, parallel with the hinge-line. 
CUCULLARIA, Deshayes, 1860. Shell elongated, suboval, moder- 
ately inflated, radiately striated, inequilateral, beaks subanterior, 
incurved, very close together, the hinge-area being very narrow 
and almost wanting in some species; hinge-line moderately 
curved with a few shorter anterior and some longer posterior 
fold-like teeth, arranged almost parallel to it ; numerous subequal 
teeth are situated below the beaks. Arca heterodonta, Desh. 
(exxvii, 80, 81). From the Paris Basin. 
NEMODON, Conrad, 1869. Shell elongated, form resembling 
Macrodon, but of thin structure ; hinge-area very narrow, hinge- 
line long, straight, or slightly curved under the beaks, “ with 
three linear teeth parallel with the anterior cardinal margin” in 
the left valve, and with a double posterior lateral tooth, being 
very long and linear; under the beaks a few granular teeth are 
present. M. Hufalensis, Conrad (cxxvi, 50,51). Scarcely dis- 
tinct from the typical Macrodon. 
GRAMMATODON, Meek and Hayden, 1860. Appears to be dis- 
tinguished only by the posterior muscular impression not being 
raised upon a projecting lamina. Jurassic; U. 8S. Type, M. 
inornata, M. and H. 
PARALLELOPIPEDUM, Klein, 1753. 
Distr.—2 sp. China. JP. tortuosum, Lam. (exxvii, 73). 
Shell subquadrangular or mytiliform, subequivalve, carinated, 
twisted so that the straight hinge-line is oblique instead of 
transverse to the beaks; teeth numerous, middle ones smallest, 
lateral ones larger and oblique. 
ScapHutLa, Benson, 1834. 
Distr.—Fresh water, India, Burmah. 
Shell thin, elongated, subtrapeziform, equivalve, very inequi- 
lateral, carinated behind; valves covered with a thin, smooth 
epidermis; hinge edentulous in the centre, posterior teeth 
laminar and branched, 
S. pinna, Benson (exxvi, 52), is found in the Ganges and its 
branches, from Calcutta to Humeerpoor on the Jumna, 1000 
miles from the sea. A second species has been found in the 
river Tenasserim, Burmah. 
Cucutua#aA, Lamarck, 1801, 
Etym.— Cucullus, a cowl, 
Distr.—2 sp. Mauritius, Nicobar, China. Fossil, 240 sp. 
Lower Silurian; North America, Patagonia, Europe. C, con- 
camerata, Mart. (cxxvii, 74), 
