High and low Dimorphisiu. 335 



I 



I the condition described by Müllek, but is never so marked nor is it 



discontìnuous , the types graduating- iuto one another. We must 



therefore adniit for the present that although the kind of dimorphism 



, described by Miller does not oceur in the Mediterranean L. duhia^ 



I there is a possibility that the Brazilian species has progressed 

 fiivther on the same lines and that the two forms of male described 

 by Müller really do belong to one species. On the other band the 

 forms discovered by me and to be now described, namely L. mer- 



I caniilis and niergellìnae and also Dollfus' form L. inermis^ corre- 

 spond very well with Müllers low male, and since these species 

 may be foimd mixed up with L. dubia, and their females are only 

 distingiiishable from L. dubia C by the less nuraber of joints in the 

 uropod, it is quite possible that Müller has mixed up two species. 

 It appears to me that the only way this matter can be settled is 

 by examining the Brazilian species. Stebbing's Suggestion that the 



.1 low male of Müller was in reality an immature form is I think 

 wroug; the immature male of L. dubia is the form whieh has beeu 

 described as L. Sariguì/i: and there is no evidence of the existence 

 vf a form intermediate between this and the adult male. L. dubia 



I occurs at Naples ali round the shore and at moderate depths, 

 especially among the coralline algae. 



L. mercantilis. — New species. — PI. 20, Figs. 18 — 23. 



Male. Length 1.5 mm., Breadth 0,25mm. Mouth parts completely 

 , degenerate as in L. dubia. P* antenna has 7 joints, sense-hairs 

 I not very numerous, about 4 to each joint of flagellum, but slightly 

 longer than in L. dubia. Eyes poorly developed. Chelae not more 

 strougly developed in male than female; bitiug edge of carpopodite 

 continuously serrated; comb has 14 bristles. Uropod has endopod 

 with 4 joints; exopod with 1 joint, longer than in L. dubia. 



Female. Length 2.75. Very hard to distinguish fiom L. dubia 9, 

 the only Constant distiuguishing features being (1) the endopod of 

 uropod has 4 joints, exopod being one jointed but conspicuous; 

 (2) P* antenna which is 3-jointed has middle joint always tinged 

 with purple. 



This species occurs in fair abundance in the Porto mercantile 

 and militare among the polyzoan Bugida 'purpurotincta on whieh 

 it feeds, the whole body containing oil drops whose colour is plainly 

 derived from the Polyzoan. In this material no other Tanaid occurs, 

 but where the Polyzoan is mixed with coralline alga, L. dubia may 



