250 NUCULIDiE. 



Animal like Yoldia ; mantle-margins slightly fringed and 

 furnished with ventral lobes; siphonal tubes united, long, and 

 slender, completely retractile ; palpi appendiculated, convoluted, 

 as long as the shell ; gills narrow, posterior ; foot deeply cleft ; 

 forming an oval disk, even-margined and striated across. 



NEiLO, H, and A. Adams, 1855. Shell transverse, gaping, sub- 

 truncated, rostrated behind; surface concentrically striated ; not 

 nacreous within ; cardinal hinge-line nearly straight. M. Gum- 

 ingii, A. Adams (cxxvi, 35). Recent. M. Monterosati, Bell. 

 Miocene ; Italy. 



TiNDARTA, Bellardi, 1815. Shell thick, globose, oval, closed, 

 beaks swollen ; anterior teeth stronger, but the posterior row 

 longer. M. arata^ Bell. Pliocene ; Asti, Italy. 



NUCULARiA, Conrad, 1869. Shell thin, not pearly, ovately 

 ■elongated, inequilateral, smooth ; beaks pointed, subanterior ; 

 teeth angular, those of the posterior line complicated. M.papyria, 

 Conrad (cxxvi, 36). Cretaceous ; Haddonfleld, N. J. 



Phthonia, Hall, 1869. 



Distr. — 2 sp. Fossil; Hamilton Group, N. Y. P. sectifrons, 

 'Conrad (cxx, 8). 



Shell thin, compressed, equivalve, transversely elongate-ovate, 

 widening posteriorly and having small obscure subanterior beaks 

 and an obscure angular umbonal ridge ; surface covered by more 

 or less distinct radiating striae or costse, which are crossed and 

 cancellated by finer concentric lines, often forming rugse or node- 

 like markings on the rays ; hinge apparentlj'^ destitute of teeth ; 

 external ligament small, elongated ; adductors small, superficial, 

 pallial line apparently entire. 



Pal^oneilo, Hall, 1870. 



Distr. — 15 sp. Palaeozoic ; U. S. P. coiistricta, Conr. P. 

 .Bedfordensis, Meek (cxxv, 25). 



Shell Nuculiform, transversely ovate or subelliptical, the pos- 

 terior end extended, often subrostrate, with a more or less 

 defined sulcus along the umbonal slope; concentrically striated or 

 ribbed ; hinge-line more or less arcuate, crenulated throughout, 

 not interrupted beneath the beak by a ligamental pit, but having 

 :an external ligament; muscular scars distant, faintly marked ; 

 : several small pedal scars within the umbonal cavity ; pallial line 

 simple or obliquely truncate posteriorly. 



Differs from Nucula in the want of a ligamental pit, in the 

 teeth being continuous under the beaks, in having an external 

 .ligament, and in the sulcus on the posterior slope. 



NucuLiTES, Conrad, 1841. 

 .Syn.—Cncu\\e\\&, M'Coy, 1851. Cleidophorus, Hall, 1847. 



