1879.] 'lightning' and 'porcupine' EXPEDITIONS. 577 



The teeth are much more numerous aad finer than in 

 L. pustulosa. 



Yoldia nana of M. Sars. 



9. Leda tenuis, Philippi. 



Nucula tenuis, Phil. En. Moll. Sic. i. p. 65, t. v. f. 9. 



L. pygmcea, B. C. ii. p. 154 ; v. p. 173, pi. xxix. f. 5. 



'Lightning' Exp.: St. 2, 3, 5, 7. 



'Porcupine ' Exp., 1869 : St. 1, 8, 13, 14, 15, 17, 18, 23a, 35, 61, 

 62, Loch Torridon. 1870 : Atl. 1, 2, 3a, 9, 13, 22, 24, off C. Sagres, 

 26-34 ; Med. 45, Cartagena B., 55, Benzert Road, Adventure Bank, 

 off Rinaldo's Chair. 



Distribution. Scandinavia to the iEgean ; 10-650 fins. 



Fossil. Pliocene and Post- tertiary. Siberia?, Scandinavia, Great 

 Britain and Ireland, Belgium ?, Transylvania ?, Biot, Italy ; 0-240 ft. 



This species was referred by Philippi in his second volume to the 

 Nucula pygmcea of Von Minister ; but the description and figure of the 

 latter species given by Goldfuss in his ' Petrefacta Germanise/ and 

 specimens of the fossils kindly sent me by Dr. Wiechmann, have con- 

 vinced me that they are different species. I have therefore adopted 

 Philippi's original name tenuis. The well-known Nucula tenuis of 

 Montagu belongs to another genus ; but Philippi did not distinguish 

 the genus Leda, and therefore changed his name for that of Von 

 Miinster. According to Forbes, N. gibbosa of James Smith is a 

 variety of the present species. L. tenuis does not appear to inhabit 

 the Arctic seas, although L. lenticula of Moller, = ro/a7a abyssicola, 

 Torell, has been mistaken for it by some authors, which makes it 

 difficult to verify all the localities mentioned by them. 



10. Leda lenticula, Moller. 



Nucula lenticula, Moll. Ind. Moll. Grcenl. p. 17. 



Yoldia abyssicola, Torell, Spitz. Moll. t. i. f. 4, a, b. 



'Porcupine' Exp. 1869 : St. 9, 23a, Loch Torridon (perfect but 

 dead and perhaps semifossil, like L. arctica). 1870 : Atl. 34, 27, 28, 

 30. Valves only. 



Distribution. Wellington Channel, Davis Strait, Dutch arctic Esp., 

 Novaya Zemblia, Norwegian arctic Exp. 1878, Shetland (semi- 

 fossil*?); 20-656 fins. 



Fossil. Post-tertiary or " glacial." Norway, Clyde beds, Siberia, 

 Labrador, Canada, Maine. 



I agree with Professor G. O. Sars that this may be Moller's 

 species ; but the description is so short and indeterminate that it is 

 almost equally applicable to L. tenuis. The late Professor M. Sars 

 regarded it as a variety of the latter species, and as the Nucula 

 gibbosa of James Smith. It is the Yoldia abyssicola of Torell, but 

 not of M. Sars. 



The present species is gibbous ; and the anterior end is much more 

 marked and upturned than in L. tenuis. 



Proc. Zool. Soc— 1879, No. XXXVII. 37 



