LEDA. 163 



Leda Jacksonii. 



Fig. 65. 



Shell ovate, convex, inequipartite, posteriorly diminishing to a narrow, as- 

 cending beak, truncated at tip, and with a flexure in the margin beneath it; sur- 

 face with concentric, elevated lines ; teeth fifteen before, and twenty beliind the 

 beaks. 



NiiculaJacksom'i, Gocld, Inv. Mass. Isted. 102, fig. 6.5 (1841). 



Lecia bnrcata, Steenstrup, in MiJller's Moll. Gra'iil. 17. — Sowerbv, Thcs. Conch. No. 



15, figs. 63, 6+. — Packard, Labrad. Mar. Anim. 13. 

 Ntictddna biiccaia, MoRCii, Prodr. Moll. Groenl. 2\ (1857). 



Shell ovate, clona-atcd, ventricose, rather solid ; beaks at the an- 

 terior third ; aiiteiiorly rounded ; posteriorly rapidly attenuated so 

 as to form a somewhat aseending Ijeak, truncated 

 at tip ; posterior liin<>-e-margin straight and sharj), '^' 



compressed at each side so as to form a Ijroad . - -.- r > 

 area defined by denticulated linos, and smooth ; 

 under the tip is a flexure or shallow indentation 

 of the basal margin, and an elevated ridge runs 

 from the beaks to the lower angle of the tip ; sur- 

 face covered with fine, crowded, elevated, conceii- L.juif.son,i. 

 trie lines ; within grooved and irregular, with ac- 

 cumulations of calcareous matter, the most remarkalde of which are 

 one under the posterior series of teeth, and a rib going to the mid- 

 dle of the truncated tip ; cartilage pit a narrow cavity, which pene- 

 trates through the shell and forms a transverse fissure between the 

 beaks, which are widely sei)arated ; series of teeth strongly curved, 

 fifteen before and twenty behind the beaks, short, very })road, and 

 folded outwardly. Length, one inch ; height, eleven twentieths of 

 an inch ; breadth, two fifths of an inch. 



Found at the land-slip at Pride's Bridge, Presumpscot River, 

 Westbrook, Maine, September, 1837 ; and also by Dr. C. T. Jackson 

 at Augusta, while engaged in the geological survey of ]\Iaine, in 

 honor of whom I have named it. Greenland {3I''irch, Moller) ; 

 Labrador, abundant {Packard). 



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

 drical. The concentric lines are finer and closer than in N. mimda 

 of first edition. In general outline it reseml)les N. rostrata, Sow- 

 erby, " Conch. Illust." Fig. 12. The denticulated boundary line of 

 the beaks, both Ijcfore and behind, is very peculiar. [Caused by 

 an erosion so as to show the orio-in of the hinge denticles. 



