THE APODOUS HOLOTHURIANS 97 



and 75-110 /J. wide. There are 12 tentacles in each specimen, each with 

 four digits; the presence or absence of a fifth rudimentary terminal digit 

 in this species and its near allies, and in Protankyra, seems to me to be a char- 

 acter depending on the state of contraction and the opinion of the observer. 

 Semper ('68) distinctly says there are no sense-cups on the tentacles, but he 

 only had a single imperfect specimen. In the Japanese specimens there are 

 five or six sense-cups on each tentacle in all of the specimens. They are small 

 and might perhaps be overlooked. 



LABroOPLAX THOMSONII. 



Synapta tliomsonii Herapath, 1865, p. 6. 



Synapta digitata from Antrim, Herapath, 1865, pi. i. fig. 5. 



Synapta hispida Heller, 1868, p. 71. 



Synapta digitata (partim) v. Marenzeller, 1893, p. 17. Anchor and plate, pi. ii, 



fig. 6. 

 Synapta thomsonii Liidwig, 1808a. 

 Synapta thomsonii Ostergren, 1898&. 

 "Synapta johnstonii Herapath," Lo Bianco, 1899. p. 476. 



Length. — 250-350 mm., with diameter, when fully extended, of about one- 

 fortieth as much. 



Color. — Like digitata. 



Distribution. — Reported from Carrickfergus, North Ireland (Herapath) ; 

 Concarneau, Brittany (Barrois) ; Naples (Ludwig) ; Adriatic Sea (v. Maren- 

 zeller). Apparently the range coincides with that of digitata. 



Remarks. — Although vouched for by such observers as Herapath and Lud- 

 wig, the status of this species is not beyond question. Marenzeller considered 

 his specimens merely as a form of digitata. Five specimens which I received 

 from Naples in 1898 as digitata all lack the sensory cups and the giant anchors, 

 while the anchor-plates are similar to those described by Ludwig for thomsonii. 

 It seems remarkable, however, that all of these specimens should belong to this 

 species, when they were probably selected at random. Certainly further study 

 of digitata and this, its nearest ally, is greatly needed. 



PROTANKYRA Ostergren, iSgSt. 



Tentacles digitate, 10-12, rarely 13 or 14. Digits two (rarely one only) 

 on each side. Cartilaginous ring wanting. Polian vessels 2-10, or rarely only 

 one. Stone-canal usually single, but rarely there are several. Stock of anchors 

 more or less branched or only finely toothed; arms usually serrate; vertex with- 

 out knobs. Anchor-plates without a handle, with numerous irregular perfora- 

 tions and with a more or less imperfectly developed bow across outer surface of 

 ])osterior end; plates and perforations also, with either smooth or dentate 

 margins. 



7 



