4 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



breed in May and the sole about the end of June. I can find no ac- 

 count of the breeding time of Limanda. P. americanus breeds from 

 the middle of February to the first week of April. 



In the summer of 1899, when P. americanus was especially plenty, 

 metamorphosed fish of two different lengths were taken in the tow. 

 These were about equally abundant. The smaller measured not over 

 8-9 mm, at the end of metamorphosis. Tlie larger was a moi-e bulky 

 fish with slightly more pigment and it was found swimming upright 

 until it reached a length of 13-14 mm., when it also turned left side 

 down. I found no specimen intermediate between the two lengths. The 

 larger, more pigmented specimens may have been either the larva8 of 

 the black-bellied variety or possibly the young of Limanda. The more 

 important specific differences between Limanda and Pseudopleuronectes 

 are the following : Tlie anterior part of the lateral line of Limanda is 

 more arched and this species has more fin-rays in both dorsal and ventral 

 fins. But it is difficult in the young fishes to establish a satisfactory 

 division on the basis of the number of fin-rays. According to Jjumpus 

 ('98), P. americanus at Wood's Hole averages 66.1 fin-rays to the 

 dorsal and 49.6 to the ventral fin. Jordan and Evermann ('96-00) give 

 for Limanda 85 dorsal and 62 ventral fin-rays. The specimens of Li- 

 manda I have counted at Wood's Hole vary from 81 to 78 in the dorsal 

 and 61 to 47 in the ventral. I counted the fin-rays in six small fishes, 

 three of each type, and found that in two of these — they belonged to 

 the 14 mm. type — the rays corresponded to the formula for Limanda, 

 and that in one (9 mm. long) they agreed with P. americanus, there 

 being 64 dorsal and 47 ventral rays. The number of rays in the other 

 three were absolutely intermediate, two (8.5 mm. long) having resj^ec- 

 tively 71-54 and 76-51 rays, the remaining one 75-56 rays. 



The work of Kyle ('98) at the St. Andrews laboratory is valuable for 

 comparison at this point. There are five dextral flounders on the Scotch 

 coast which may be confused with one another. Tlie ones most like 

 our species are Pleuronectes flesus, the flounder, P. platessa, the plaice, 

 and P. limanda, the dab. Of these, when metamorphosis is completed, 

 the flounder is the shortest (about 8 mm., according to Petersen), the 

 plaice next and the dab the longest. The plaice may vary in length 

 from 13 to 16 mm. ; the dab from 16 to 19 mm. at metamorphosis. 

 In Danish waters (Petersen, '94, p. 14) the metamorphoses of these two 

 species are complete when the fish is from 4 to 6 mm. shorter. 



As the plaice and dab overlap each other in length, their fin formula) 

 were ascertained by Kyle in the hope of finding there a distinctive 



