THE BAKKACLES IN THE U. S. NATIONAL MUSEUM. 18 



-shape of the median lateral plates, which are also situated lower. 

 S. (jrimaldi Aurivillius, from the Azores in 845 to 1,230 meters, 

 which has not yet been figured, is probably ev^en nearer our west 

 Atlantic species, but it differs by the straight carina, the shorter sub- 

 carina, only a third the length of the rostrum, and by having the apex 

 of the carina intruding a little l)etween the terga. Until a full descrip- 

 tion and figures are pul)lislied, the exact relationship of S. (jrimaldi 

 to S. superhum can not be determined. 



In the figured t3^pe of S. supei'ljum the upper latus on the side 

 shown is a little abnormal in having an erect apex. It is normally 

 incurved on the other side of the same specimen, as shown on the 

 right side of the dorsal view. The peduncle, too, is broken off short 

 in this example. 



II. Subgenus SMILIUM Gray. 

 1825. Smilium Gray, Annals of Philosophy, newser., X, p. 100 {S. peroniion\y). 



Upper latus occupying the space hettoeen scutum and carina^ helow the 

 terguiH^_ two or three pairs-oflatera^ with rostrmn and sid>carina forming 

 the lotoer whorl of plates. Plates 13 or 15. Complemental male having 

 a, normal pyedtincle and capitulum ^ fl"- latter with plates. Type., S. 

 perovil Gray. 



In this group the position of the upper latus and the general struc- 

 ture of the capitulum approximate to the condition in typical Scalpel- 

 Uaiu; but the presence of a subcarina and the primitive PoUicipes-X^kQ 

 male indicate greater affinity to the subgenus Calantica. The known 

 species may be grouped as follow^s: 



a. Valves 13, inframedian latera wanting; male •with triangular capitulum and six 

 well-developed valves. <S'. jieronii Gray, S. scorpio Aurivillius, S. scxrorimfuin 

 Pilsbry. 

 aa. A^alves 15, three pairs of basal latera being present; male more degenerate, with 

 oblong capitulum and three small valves. 



h. Carina angularly bent; umbo of scutum not apical. S. rostratum Darwin, 



S. rend Gruvel. 

 bb. Carina bowed, with apical umbo; umbo of scutum apical. S. squamu- 

 liferum Weltner, ^S'. stratum. Aurivillius, S. bengalense Annandale. 



These forms are oriental and austral in distributioii, and none are 

 represented in the U. S. National Museum collection. 



III. Subgenus SCALPELLUM, s. str. 



Valves lisually wJwlly caldiied; carina visually angularly hent., with 

 the umho removed from the apex; inframedian latus wide throughout^ 

 the innho at or heloic the middle of its height; males sacJcllke., not divided 

 /)ito capituluDi and peduncle., with minute valves or none. Tyj)e., S. 

 scalpellum.. 



This series is chieth' characleiized by the broad inframedian latus, 

 with facets of the wide summit against both scutum and upper latus, 



