of the postclavicle in this juvenile specimen is 5.15 mm long and 3.20 mm broad. 

 The posterior half is 9.25 mm long and 2.60 mm broad. The demarcation between the 

 lamellate and needle-shaped portions of the posterior portion is not clear, but it 

 is much longer overall than in mature fish. The total length of the specimen is 

 100 mm, 90 ram without the caudal, and the depth is about 20 mm. 



In the Plecostei as a whole, the preopercle in the larval stage has two rows 

 of spines, one anterior and one posterior, but in the postlarval stage the anterior 

 row disappears and the posterior row generally becomes minute. The mouth is at its 

 largest in the middle period of the larval stage when it extends posterior to the 

 posterior edge of the eye. The snout is also at its longest in this period. The 

 opercle is very narrow during the larval stage, but as the fish approaches the 

 juvenile stage it gradually broadens until its shape resembles that of the mature 

 fish. At the beginning of the juvenile stage serrations begin to develop in the 

 middle of the posteriodorsal edge of the opercle, extending thereafter to the limit 

 of the posterioventral edge. Serrations are also seen on the posterior edge of the 

 subopercle and on the ventral edge of the interopercular. These serrations are a 

 characteristic of the Plecostei from the juvenile stage on, and they appear never to 

 have been seen in the Cybiidae and Scombridae, although some serrations have been 

 noted on the isomaguro QGymnosarda nuda j but only on the posterior edge of the 

 opercle. Furthermore, the forked shape of the anterior projection of the subopercle 

 in the Cybiidae has never been seen at any stage of development in fishes of the 

 Plecostei. 



In Volume 2 (Biology) of the Report of the Danish Oeeanographic Expedition to 

 the Mediterranean and Adjacent Seas in 1908 -10, which was published December 31, 

 1924., under the heading "Scombriformes", Ehrenbaum reported the results of research 

 on the material collected during three years by the exploratory vessel "Thor" This 

 paper, with four folding plates and 12 pages of text, is very important, and can 

 be said to be almost the only one dealing ivith the larval forms of the Plecostei. 

 It is very difficult to obtain larval and juvenile specimens of these fishes and it 

 Is even more difficult to determine to what species they belong. Ehrenbaum' s clas- 

 sification emphasizing the number and shape of the vertebrae is good, but unfor- 

 tunately his material was almost all larval forms with no reference to juvenile and 

 mature specimens, and consequently his specific identifications are somewhat un- 

 satisfactory. The paper takes up mackerel, Sarda orientalis, tuna, albacore, skip- 

 jack, Euthvnnus yaito . and Auxis sp. The author says that he rarely took larval 

 fish over 10 mm and none at all over 15 mm. In effect, during the larval stage the 

 fish are not very active and can be taken in plankton nets, but when they reach the 

 juvenile stage they are very active swimmers and do not get Into plankton nets. 

 The small juvenile specimens which I have been able to get were all recovered from 

 the stomachs of fish taken by the Kagoshima Prefecture research vessel Shoyo Maru, 

 and these are few in number. A special net designed to catch juvenile fish has 

 been used, but it has not yet proved effective. It is rather unreasonable to try 

 to pull a fine-meshed net at high speeds. When the mature fish of the Plecostei, 

 which are among the fastest swimmers, are feeding on the juveniles of other kinds 

 of fish, it is not unusual to find twenty or thirty individuals in the stomach of 

 one fish, but when they are feeding on the juveniles of their own kind, only a few 

 specimens at most are found in any one stomach, fle are going to try new methods of 

 collecting this year too, but we believe that looking for specimens in the stomachs 

 of skipjack, tuna, and dolphins on the skipjack fishing grounds is still a con- 

 venient method. 



I am seeking particularly larval forms of skipjack and tuna about one inch in 

 length, and I request the assistance of any of my readers who may have opportunities 

 to obtain such specimens. 



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