1. DITREMA 240 



than the orbit. The dorsal fin commences vertically above the root 

 of the ventrals : the first spine is very short ; the three following 

 increase in length, the three last being the longest, of nearly equal 

 length, half as long as the head ; the anterior rays a little longer 

 than the last spines. The anal fin commences below the seventh 

 dorsal ray, and extends further backwards than the dorsal fin, its 

 spines being very distinct ; caudal fin emarginate. 

 Back daz'k-greenish-olive, belly silvery. 



10. Ditrema minimum. 



Micrometrus mmmnis,Gibhmis,Proc.Aca(I.Nut. <S('. P/uVrtrf. ] 854, p. 125; 



Afftm. Proc. Bost. Soc. N( '. Hist. 18G1, p. 121). 

 Cymatogaster m'miniii«, Gibbons, L c. p. lOG. 



Holconotus trowbridgii, Girarcl, Proc. AcadNat. Sc. Philad.l8f)4:,Y>. 152, 

 Abeona trowbridgii, Girard, I. c. 1855, p. 322, and U. S. Pacif. R. R. 



Exp. X. Fish. p. 186. pi. .34. figs. 6-10. 



D. ^". A. -^. L. lat. 42. L. transv. 4/13. 



14 15-10 ' 



The middle dorsal rays are longer than the posterior. Scales on 

 the cheek in three series. .The height of the body is contained twice 

 and a third in the total length (without caudal). Jaws equal in 

 length anteriorly ; lips thin, the fold of the lower being continuous 

 round the jaw. 



a. Four and a half inches long. San Francisco. From the Boston 

 Museum. 



11. Ditrema arcuatum. 



Hyperprosopon arcuatus. Gibbons, Proc. Acad. Nat. Sc. Philad. 1854, 



p. 125; Af/ass. Proc. Bost. Soc. Nat. Hist. 1801, p. 133. 

 argenteuin, var., Gibbons, I. c. 1854, p. 106. 



D. ^. A. i . L. lat. 74. L. transv. 8/20-21. 



Eye very large, longer than the snout, its length being one-third 

 of that of the head. The profile of the occipital region is concave. 

 The middle dorsal spines are longer than the posterior and than the 

 soft rays. Scales on the cheek in four scries. The height of the 

 body is contained twice and a fourth in the total length (without 

 caudal). The lower jaw longer than the upper ; the maxillary ex- 

 tends slightly beyond the vertical from the anterior margin of the 

 eye. The cleft of the mouth does not extend upwards to the hori- 

 zontal from the upper margin of the pupil. Lips thin ; the fold of 

 the lower continuous round the jaw. Ventral black posteriorly. 



a. Adult. San Francisco. From the Boston Museum, as Hyper- 

 prosopon argenieum. 



12. Ditrema megalops. 



Hyperprosopon argeuteum. Gibbons, Proc. Acad. Nat. Sc. Philad. 1854, 



pp. 105, 125; Afjuss. Proc. Bost. Soc. Nat. Hist. 1861, p. 132. 

 Holconotus megalops, Girard, Proc. Acad. Nat. Sc. Phihid. 1854, p. 152. 



