| Summary: | A great many Tursiops sp. and Pseudorca crassidens were caught at Arikawa Bay in Goto Is. of Nagasaki pref., and they were observed and measured about many points. The results of the observation and measurement about Pseudorca crassidens were compared with that of the other sea areas and the characteristics of this species were investigated. 1) It is made clear by their size distribution that the shoal of this Pseudorca sp. had formed the harem. 2) The body color is brown black in all over the body, but a slender white line exists at the breast from the navel along the central line and it melts away in a light grey uncertain pattern which exists between the both pectoral fins. 3) The front of the head makes slender to some extent in egg form, and the lower jaw retires considerably than the upper jaw and the mouth rift is straightly from the lower front to the upper rear. 4) The front edge of the pectoral fin makes the loose wave and there are two mounds in this part. 5) They have not the sickle-shaped dorsal fin, and the top of the dorsal fin is very roundish and turns to backward. 6) The rift at the notch of the tail is deep, and both tail fins are piled up in this point. 7) The many fetus about 80cm in body length were discovered in this investigation. 8) The stomach contents were filled up by the squid, it is clear that this Pseudorca crassidens was the shoal of feeding migration and not breeding migration from the stomach contents, the body length of fetus and the date of catch. 9) It is made clear by the result of the measurement of the body external proportion that in this species the head part is smaller and the caudal fin is larger than that of the other sea areas. 10) About the change of external proportion with the progress of growing it is made clea that the growth of the back part of the dorsal fin is more better than that of the front part. 11) It is made clear by the result of the measurement of the skull proportion that in this species the snout part of the skull is more slender in some extent and ...
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