282 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 57. 



Cat. No. 



173595 

 11888 

 110967 

 274154 

 173597 

 173598 

 173599 

 173600 

 17818 

 173594 

 173596 



Locality. 



Mediterranean . . 

 Mediterranean . . 

 Mediterranean . . 

 Mediterranean . . 



Coast of Tunis 



Bay of Naples . . . 



Bay of Naples 



Bay of Naples . . . 



Sicily 



Port Vendres 



Adventure Bank, 



40-20 fathoms. 



A careful comparison of all the specimens available has enabled me 

 to add something to Davidson's description of the interior of this 

 species. 



The cavity of the beak in the attached valve in fully-developed 

 specimens shows a median septum supporting on each side an 

 excavated plate which anteriorly projects more or less beyond the 

 septum in a prong or point. In some specimens the septum only 

 appears deep in the valve; in others it is prominent at the commis- 

 sure between the plates and rises between them as a keel. In the 

 fullest development of the arrangement the septum rises to the 

 upper vault of the beak, thus dividing the cavity, in combination 

 with the plates ("coques" of Lacaze Duthiers), into four compart- 

 ments. The space between the forward prolongation of the plates 

 is not deep, but triangular, and in none of the specimens which I 

 have examined have I seen anything resembling the squarish or 

 bilobed plate figured by Davidson (pi. 23, fig. 14 and fig. 15h). I 

 presume in these cases the prongs have been broken off. One of the 

 characters used by Allan Thomson to separate his Theddellina from 

 Lacazella is the presence of prongs in the former, but, as above 

 stated, the prongs are quite evident in any well-preserved specimen 

 of the type of Lacazella mediterranea. 



LACAZELLA MAURITIANA, new species. 



This species has a remarkable resemblance to the preceding, with 

 which it has been confounded, but differs by having in the apical 

 cavity of the attached valve instead of a platform supported by a 

 septum, only two long, slender, excavated, upturned processes com- 

 pletely isolated medially, with no sign of a septum. The outer sur- 

 face is minutely regularly granular. In other respects it agrees closely 

 with L. mediterranea. 



Type.— Cat. No. 173593, U.S.N.M. 



