432 ECHINODERMS OF THE BRITISH ISLES 



pigment. Very small form, scarcely more than 1 cm. long. It 

 is viviparous, the young ones developing in the body cavity. 



The anchor plate may be incomplete at the articular end, 

 the two 'outer holes wanting. Such plates then have the shape 

 characteristic of the genus Labidojdax, with a narrow handle. 

 L. minuta in reality occupies an intermediate position between 

 the genera Leptosynapta, Labidoplax, and Rhahdomolgus . 



Hitherto known only from off Heligoland, where it occurs on 

 muddy bottom, ca. 20 m. 



2. Labidoplax Ostergren. 



Basal part of the anchor plate has the shape of a narrow 

 handle, sharply set off from the outer part of the plate. Tentacles 

 with only 1-2 pairs of digits. 



Three species of this genus know n from the British seas ; a 

 fourth, Labidoplax media Ostergren, known only from off Bergen, 

 may well be expected to occur there also. 



Key to the species oj Labidoplax known from or likely 

 to occur in the British seas. 



1. Tentacles 11, with a long terminal and 1 pair of smaller lateral 



digits. Gonads simple tubes . \. L. Buski (M'Intosh) 



Tentacles 12; no terminal digit, but 2 pairs of lateral digits at 



the end of the tentacle ....... 2 



2. Anchor plate of regular shape (as in L. Buski, Fig. 264). Gonads 



branched. Small form, 3-4 cm. long.^ . L. media Ostergr. 



Anchor plate of irregular shape ; large forms, up to 30 cm. 



long , . . . . . . . . .3 



3. Anchor plates in anterior end of body thick and of complicated 



structure, with serrate edge ; handle short and broad, with 



several small holes . . . 3. jL. T/^omso?^^ (Herap.) 



Anchor plates all flat, simple, w4th edge smooth ; handle narrow, 



with an elongate, slit-like median hole . 2. L. digitata (Mont.) 



1. Labidoplax Buski (M'Intosh). (Fig. 261.) 



(Syn. Synapta tenera Norman.) 



Tentacles 11 (very rarely 10 or 12), with one pair of lateral 

 digits and a very long terminal digit. The alimentary canal 

 forms a short loop in the middle of the body ; the ascending 

 part is connected w ith the first descending part by a transverse 



1 For a detailed description of Labidoplax media cf. Hj. Ostergren, 

 " Zur Kenntniss der skandinavischen u. arktischen Synaptiden ", Arch. 

 Zool. exper. et gener. (4), iii., 1905, p. clviii. 



