250 Mr. C. P. Sisjerfoos on the PholadidaR. 



'fa 



anterior palatine foramina 6'5 x 2*7 ; length of upper molar 

 series 5' 7. 



Hah. Jampea Island, Saleyer group. 



Coll. A. H. Everett, Dec. 1895. 



A second specimen (female) has its head and body 125 

 millim., tail 169, hind foot 29*5, and ear 18. 



This species seems to be most closely allied to Miis Bec- 

 carii^ Jent., from which it differs by its rather larger size or, 

 at least, longer hind feet, the absence of any terminal pen- 

 cilling to the tail, its grey-mixed belly, white feet, the normal 

 projection forward of the zygoma-root, and the further exten- 

 sion backward of the anterior palatine foramina. 



XXXTX. — The PholadidaB. — II. Note on the Organization of 

 the Larva^ and the Post-larval Development of Ship-v^orms. 

 By C. P. SiGEEFOOS*. 



A YEAR ago I published f f^ note on the early stages oE 

 development of the Pholadidffi, in which the breeding-habits 

 of Pholas and three species of ship-worms were described. 

 During June and July of 1895 I again visited Beaufort, N. C, 

 with the Johns Hopkins Marine Laboratory, and collected all 

 stages of one of these species [Xylotrya fimhriata) from the 

 small bivalve that has just become attached to the adult. As 

 the eggs of this species are extruded freely into the water, I 

 have not been able to observe the stages between the oldest 

 larvEe raised in aquaria from artiticially fertilized eggs and 

 the attached stage, in which the development is much more 

 advanced. For these intermediate stages it is necessary to 

 resort to species which retain the embryos in the gills. 



The free-swimming stage is reached in three hours, and in 

 a day a well-developed shell has been formed. The young 

 of Lamellibranchs develop but slowly, and though we have 

 no direct observations as to the time the ship- worm larva is 

 free-swimming, we may assume, I think, that it is at least a 

 month, it may be two. During this time most of its energies 

 are expended in locomotion, while after it has become 

 attached it may devote all of its energies to forming its 

 burrow and to securing food for itself ; so that its rate of 

 growth is very rapid. The larvse become attached very 



* From the 'Johns Hopkins University Circulars' for June 189(5, 

 pp. 87-89. 



t ' Johns Hopkins University Circulars,' no. 119, June 1895 ; Ann. & 

 Mag. Nat. Hist. [«] xvi. p. 233 (189.5). 



