REPORT ON THE PTEROPODA. 15 



Key to the Species. 



I. The two distal lateral suckers of the median appendage larger than the two. 

 proximal ones. 



1. The lateral acetabuliferous appendages still distinct, . . Dexiobranchxa ciliata. 



2. The lateral acetabuliferous appendages atrophied, . . . Bexiobranchsca minuta. 

 II. The four lateral suckers of the median appendage of the same size. 



1. The median appendage atrophied, .... Bcxiobranchsea simplex. 



2. The median appendage well developed. 



A. The suckers corresponding to the lateral appendages disposed in 



one row, ....... Bexiobranch&a paucidens. 



B. The suckers corresponding to the lateral appendages disposed in 



two rows, ....... Bexiobvanchsea polyeotyla. 



*1. Dexlobrancliaea ciliata (Gegenbaur) (PI. I. fig. 1). 



1839. (?) Pneumodermon mediterraneum, van Beneden, Exercices zootorniques, pi. iii. fig. 3. 

 1855. Pneumodermon ciliatum, Gegenbaur, Untersuchungen iiber Pteropoden und Heteropoden, 



p. 74. 

 1862. Pneumodermopsis ciliata, Bronn, Die Klassen und Ordnungen des Thierreichs, Bd. iii. 



p. G19. 

 1886. Bexiobranchxa ciliata, Boas, Spolia atlantica, K. dansk. Vidensk. Selsk. Skriv., 6 Rajkke, 



Bd. iv. p. 159, pi. vii. fig. 104. 

 1 886. Bexiobranchxa improvisa, Boas, Spolia atlantica, p. 1 60. 



Foot. — Posterior lobe very long and pointed. 



Lateral Gill very long. 



Buccal Appendages. — The lateral appendages are still present, but very sbort ; 

 they have the form of a horizontal projection on each side of the ventral wall of the 

 buccal cavity, and each projection bears on its free edge from six to nine suckers of 

 moderate size. The five suckers corresponding to the median appendage are as follows : — - 

 the median distal sucker is larger than those of the lateral appendages ; of the four other 

 suckers, the anterior (distal) pair is formed of two very large suckers (much larger than 

 the last one), placed on long thin peduncles, and with a broad ledge having a pointed 

 beak on the side opposite to the insertion of the peduncle. 1 The suckers of the 

 posterior (proximal) pair are of about the same size as the suckers of the lateral 

 appendages. 



Raclula. — Formula 7:1 : 7 ; the median tooth tricuspid. 



Hook-sacs with from thirty to forty hooks. 



Colour. — Greyish- violet. 



Length. — Not larger than 1 cm. 2 The specimen figured is a little contracted at its 

 posterior part. 



1 Boas, Spolia atlantica, pl.viii. fig. 113. 



2 The measurements given in this Report are always from the buccal aperture to the posterior extremity of the 

 body, excluding therefore the evaginable parts of the mouth, namely, the proboscis, buccal appendages, and hook-sacs. 



