268 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



was suggested by Hollard, merely as exaggerations of the crests aud 

 ridges which define the lateral, dorsal, and ventral surfaces of the caraT 

 pace, occurring in those parts of the body and in that part of the above 

 series where these crests aud ridges are most emi)hasized, and their ab- 

 sence coinciding with the absence of prominent lines of demarcation. 

 They are most numerous in the middle portion of the above series, in 

 the forms transitional between the triagonal and tetragonal sections of 

 the genus, and are alike also at both extremes. 



The geographical distribution of the species is interesting in the light 

 of this gradation. The triagonal forms (I and II) occur only in the West 

 Indies. The next in order (III) occur not only in the West Indies but 

 in the southeastern Atlantic. The subtriagoual form {IV) is represented 

 in the southeastern Atlantic (at the Cape of Good Hope), in the west- 

 ern Pacific (China), in Australia and the East Indian Archipelago. The 

 subtetragonal forms (V) are represented in the Indian Ocean, west to 

 the Cape of Good Hope, in Japan and Australia, and in the East Indian 

 Archipelago, while the tetragonal forms (YI, VII, and YIII) almost ex- 

 clusively in the Indian Archipelago and the Indian Ocean. 



There is no dearth of names for the sections of this group, but as has 

 been remarked, it is impossible to assign them or subdivide the genus 

 by any but arbitrary methods. 



Swainson's Ostracion corresponds to Divisions VI, VII, and VIII; 

 his Tetrosomus to Divisions IV and V, although he assigns 0. cornutus 

 to the following genus; his Lactophrys to Divisions II aud HI, aud his 

 Ehinesomus to Division I. 



Kaup's Ostracion would include Divisions I, II, HI, and IV ; his Lac- 

 tophrys, Division V; and his Cihotion, Divisions VI, VII, and VIII. 

 Bleeker's Ostracion includes I, VI, VII, aud VIII; his Tetrosomus, IV; 

 his Acanthostracion, II, HI, and V. 



Dr. Bleeker by assuming Division V, instead of Division I, as one ex- 

 treme of the series, made his division of the group into subgenera more 

 plausible. This arrangement does not, however, allow as com2)lete a 

 gradation of form. 



SuBOEDER OSTRACODERMI,* Gill. 



Synonym as family name. 



<^ Sclerodennes, Cu\^er, Regne Animal. 1st cd ii, 1817, p. 153; 2(1. ert. ii, 1829, p. 375. 



< Sclerodermi, Gunther, Cat. Fisli. Brit. Mus. viii, 1870, p. 207. (Sjuonym as sub- 



ordinal name.) 



< Sclerodermcs, Hollakd, Ann. Sci. Nat. (4) xiii, 1860, p. 31. 



Synonyms as ordinal names. 



< Sclerodermi, Boxapakte, Giorn. Accad. di Scienze, lii, 1832 (Saggio Distrib. Metod. 



Animali Vertebr. a Sangue Freddo, ji. 39). » 



** The synonymy of tbis suborder is in substance quoted from Gill. MS. 



