110 PROCEEDINGS OF THE ACADEMY OF [April, 



Scalpellum aurivillii these latera are very much reduced, and in some 

 cases are displaced, lying free over the adjacent rostral latus, which 

 actually comes in contact with the carinal latus. ^ The considerable 

 number of species showing this reducting of the inframedian latera 

 gives ground for the belief that an 1 1-valved type of Scalpellum will 

 eventually be evolved, if indeed it does not already exist. 



The following groups with partially calcified valves have been 

 derived from the Arcoscalpellum stock. 



The section Mesoscalpellum Hoek, type S. javanicum Hoek, consists 

 of partially calcified barnacles which are shown by their ontogeny, 

 now known pretty fully in a few forms, to be descended from fully 

 calcified forms of Arcoscalpellum, like S. idioplax or S. carinatum. 

 The evidence at hand indicates the existence of several collateral lines, 

 probably derived from as many normal species, so that the group is a 

 polyphyletic one. The early post-larval stages in at least two species, 

 which I have worked out and figured («S. larvale and S. japonicum), 

 are indistinguishable from Arcoscalpellum. 



Mesoscalpellum will include, for the present, besides the forms 

 described in Hoek's Siboga report, the group of S. intermedium (S. 

 intermedium, S. nipponense, S. laccadivicum) , the group of S. japonicum, 

 the group of S. larvale, and that of S. gruveli {S. gruveli, S. imperfectum, 

 S. sanctcebarhane) . 



The section Neoscalpellum Pilsbry, type S. dicheloplax, contains the 

 most modified of the imperfectly calcified forms, — bizarre, skeleton- 

 like creatures with all the paired plates reduced to narrow, diverging 

 rami. 



The early stages are not known, but half-grown individuals show an 

 approximation to the condition of adults of the S. japonicum group, 

 so that a common origin is probable, and it may be found superfluous to 

 retain Neoscalpellum as a separate section. The species are widely 

 scattered geographically, and all inhabit abysmal depths. 



S. edwardsi Gruvel. Azores, 4,255 meters. 



S. dicheloplax Pilsbry. Off Eastern United States, 1525-1544 fathoms. 



S. phantasma Pilsbry. Off California, 2196 fathoms. 



;S. marginatum Hoek. Off New Guinea, 5640 fathoms. 



The nearly simultaneous publication of some 32 new species of 

 Sccdpellum by Dr. Hoek and 38 by myself, in 1907, has resulted in 



See Bull. 60, U. S. Nat. Mus., p. 65, fig. 26. 



