1908.] NATURAL SCIENCES OF PHILADELPHIA. 109 



The restricted subgenus Scalpellum is undoubtedly a natural group, 

 well characterized by the development of a large inframedian pair of 

 latera. The umbones of the carina and scutum are frequently removed 

 from the apices of those plates, but this is a variable character. 

 Two species, S. inerme Annandale and S. patagonicum Gruvel, have the 

 plates imperfectly calcified. The following species belong here: 



Group of S. scalpellum : 



S. stearnsi Pilsbry. S. patagonicum Gruvel. 



S. inerme Aimandale. S. gibbum Pilsbry. 



S. calcaratum Aurivillius. S. gibberum Aurivillius. 



S. hamatum Sars. S. ornatum (Gray). 



S. scalpellum (linne). S. salartice Gruvel. 



Group of S. calif or nicum: 

 S. californicum Pilsbry. S. osseum Pilsbry. 



Group of S. strocmii : 



S. stroemii Sars. S. s. latirostrum Pilsbry. 



S. s. obesum Aurivillius. S. pressum Pilsbr}'. 



S. s. luridum Auri villus. S. groenlandicum Aurivillius. 



S. s. aduncufn Aurivillius. *S. angustum Sars. 



S. s. septentrionale Aurivillius. S. nijmphocola Hoek. 



S. s. subsiroejnii Pilsbry. *S'. cornutum Sars. 



Subgenus Arcoscalpellum Hoek. 



All of the other species described as Scalpellum form a group sys- 

 tematically equivalent to the restricted subgenus Scalpellum, but the 

 great number of species, including several phyla with degenerate, partly 

 chitinous plates, may make it expedient to recognize several sections 

 by name. 



Arcoscalpellum Hoek,* type S. velutinum Hoek (fig. 1, i, j), includes 

 all of the species of Sections IV and V of my paper on National Museum 

 Barnacles, pp. 25 to 68, and all of those included in Arcoscalpellum in 

 Hoek's Siboga report, pp. 85 to 120, besides various other allied forms, 

 previously known, which need not be enumerated here. 



There is a distinct tendency in certain forms of Arcoscalpellum 

 towards the evolution of a phylum which will have only eleven plates, 

 by elimination of the inframedian latera. In iDarnacles of the group of 



* Arcoscalpellum is exactly equivalent to Holoscalpelhon Pils.. Bull. 60, U. S. N. 

 Mus., p. 25, published a few days later than Hoek's work. 



