ART. 10 NOTES ON MYCTOPHINE FISHES PABR 35 



of the Bingham Oceanographic Collection (see Parr, 1928, pp. 131- 

 135, and fig. 25), which differs, however, in having the PLO much 

 nearer to tlie pectoral fin than to the lateral line, and in having the 

 Pro confluent with the posterior AO. Specimen No. 2146 B. O. C. 

 also shows 6 photophores in the postero-anal series and further ap- 

 proaches B. " theta " in having a somewhat, though not very con- 

 spicuously, increased interspace between the last AO posterior and 

 the first Prc^^ but also differs in the lower positions of its PLO^ 

 upper ^AO^ and Pol.^^ The discordance between the various speci- 

 mens with 6 posterior AO^ and the consequent impossibility of basing 

 a recognition of a separate species or subspecies " theta " on this fea- 

 ture, is further increased when we also include the type specimen of 

 D. " iwotoculus " in our considerations. 



The type of D. " 'protoculus " agrees with the type of D. " theta " 

 in having 6 posterior AO^ well separated from the Prc^ and in hav- 

 ing the VLO nearer to the base of ventral fin than to the lateral line. 

 It differs from D. ''Hheta^'' however, in having the first anterior AO 

 slightly but distinctly elevated (see the diagram), in having the 

 PLO, VLO^'^ upper SAO, and the Pol inserted conspicuously lower 

 than in the type of the said form, and in having the SAO arranged 

 in an obtuse angle with the interspace between the second and third 

 organ much greater than that between the first and second. Accord- 

 ing to Taaning's synopsis this species should thus seem related to 

 D. mollis Taaning, but the difference from the other specimens of 

 the raflnesquel-tjpe, investigated by the author, with regard to the 

 length of the maxillary, which is used by Taaning as a diagnostic 

 character, is altogether too slight to be considered taxonomically 

 significant; and it is, unfortunately, impossible to give any state- 

 ments concerning the size of the luminous scale at PLO or the accu- 

 rate positions of the suborbital organs on account of the shrinkage of 



30 The discontinuity of the two series is sliown as slightly too distinct in the diagram- 

 matic illustration of this specimen (Parr, 1928, fig. 25), while it is very distinct and 

 conspicuous in the type of D. " theta." 



^ The previous statement (Parr, 1928, p. 132) that specimen No. 2146, B. O. C, agrees 

 " fairly well " with the definition of D. holti Taaning in having the upper SAO and Pol 

 " about equidistant from the lateral line and the ventral row of photophores " is based 

 upon the vertical distance above the horizontal level of the next following organ in the 

 ventral series (first anterior AO and first posterior AO, respectively), and is merely of 

 relative and approximate value, being absolutely accurate only of the Pol, while the upper 

 SAO, though distinctly lower than in specimen No. 2147, B. O. C, and much lower than 

 in specimen No. 2148, B. O. C, is still somewhat above the point of equidistance between 

 the two morphological levels referred to. 



^ The specimens are too small and too old to give accurate measurements, but in spite 

 of the fact that the VLO is also in D. " theta " considerably closer to the ventral fins 

 than to the lateral line, the VLO is still conspicuously lower in the type of D. " protocu- 

 lus," as will appear from an inspection of the accompanying diagram. The same also 

 holds good of the PLO, which in D. "theta" is only slightly below midway between the 

 base of pectoral fin and the lateral line, while it is much closer to the former in D. 

 " protoculus." 



