ARCACEA. MOLLUSCA. NUCULA. 103 



It is remarkable for its great width, which makes it almost cylindri- 

 cal. The concentric lines are finer and closer than in N. miniita. In 

 general outline it resembles N. rostrata, Sowerby, " Conch. Ulust." 

 f. 12. The denticulated boundary line of the beaks, both before and 

 behind, are very peculiar. 



NuCULA NAVICULARIS. 



Shell small, fragile, crescentic, sub-equilateral ; surface smooth ; 

 epidermis light-green ; rounded before, slightly truncated behind ; 

 umbones tumid ; teeth eight before and ten behind the pit. 



State Coll., No. 288. Soc. Cab., No. 2341. 



Nucula navicularis, Couthouy ; Bost. Joiirn. JVat. Hist., ii. 178, pi. 4, f. 4. 



Shell small, thin, fragile, of a crescentic, or somewhat kidney- 

 shaped form, smooth, tumid at the beaks, and compressed at the 

 sides, slightly gaping at both ends ; beaks very nearly central, 

 prominent, and directed backwards ; anterior side elliptically 

 rounded ; posterior side somewhat narrowed and compressed, 

 and very slightly truncated ; basal margin strongly curved ; sur- 

 face smooth, with very indistinct lines of growth ; epidermis a 

 light pea-green, thin, with many eroded spots. Ligamentary 

 fosset broad, prominent, and oblique ; teeth about eight before 

 and ten behind the fosset. Interior glossy white ; margin simple. 

 Length ^^ inch, height g^j inch, breadth 2^xy inch. 



Found in the stomachs of fish caught off Nahant and Plymouth ; 

 not conmion. 



This small shell might at first be regarded as the young of some 

 other species. But the central position of the beaks, the number of 

 teeth, and its crescentic or boat-shaped form are good characteristics. 

 The size above indicated is about one third larger than that of the 

 specimens usually found. 



Nucula proxima. 



Shell oblique, ovate-triangular, anterior side perpendicular to 

 the base ; crossed by minute, concentric, and radiating lines ; epi- 

 dermis olivaceous ; within pearly, margin crenulated ; teeth, tioelve 

 before and eighteen behind the beaks. 



Figure 63. 



