TESCH— PTEROPODA AND HETEROPODA 177 



bands. The fin on the other hand exhibits very clearly the two crossing systems (figs. 2, 4), 

 generally met with in Carinaria; it is composed of two plates, slightly converging from 

 the base of the fin towards the undermost margin. Each of these plates consists of a 

 system of parallel, separate muscular bands, stretching vertically from the base of the 

 fin towards the margin, and in their course gradually becoming thinner, some towards the 

 end dividing into two tiny branches. In the proximal part of the fin these bands are 

 directed somewhat forward. Beneath this system lies another, constituted of stronger 

 bands, which are fewer in number than those of the first system, all running across from 

 the base and directed distally. I have not been able to make out whether this last system 

 is double, like the first ; it seemed to me as if it was not double. These bands do not 

 branch towards the extremity, but anastomose now and then or are forked at their origin. 

 At the hinder margin of the fin, near the base, is placed a small sucker (fig. 4, s), from the 

 convex side of which radiate some tiny muscles. 



So the whole structure is very like that of the fin in Carinaria, and in Pterosoma the 

 same delicate network of crossing muscular bands is also a striking chai-acter of the 

 swimming organ. 



The eyes are rather large, with a broad base and the same distribution of areas devoid 

 of pigment, as in other Carinariidse. At the front margin of the eye, somewhat nearer to 

 the median line, is situated a tentacle. Now it is a curious fact, that I have again to 

 record the total absence of the right tentacle, of whicli no trace could be detected, while 

 the left was clearly developed (fig. 1, t). Perhaps this is a constant character, generic 

 or specific, as on a former occasion* a right tentacle was not found by me in this species. 



The mouth is surrounded by an annular musculature, in the same manner as in 

 Cardiapoda. Two salivary glands (fig. 1, sg), of a rather long, cylindrical shape, open 

 into the buccal cavity dorso-laterally, and are sharply bent ventrally towards their blind 

 endings. In the mouth itself, the two longitudinal folds situated at the dorsal roof and 

 slightly converging distally indicate the beginning of the oesophagus ; the folds are 

 toothless, as in other Carinariidse. The radula, at either side of which a cartilaginous 

 attachment for the radula-muscles is found, as formerly described by met in Atlanta 

 (indeed they occur in all Heteropoda), consists of 35 transverse rows, all of the usual 

 formula 2. 1. 1. 1. 2. The plates agree in most respects with those of Carinaria and 

 Cardiapoda ; the intermediate plate has the typical crest (fig. 5a, ip)\, the first and 

 second lateral plates (1st Ip, 2nd Ip) are of nearly equal length and elegantly curved, 

 while the central plate (fig. 5, cp) exhibits the usual three cusps. In the proximal rows 

 of the radula, these cusps of the central plate are very unequal, the middle one being by 

 far the largest. I have figured such a plate of the 6th row {cp'). More distally the lateral 

 cusps of the central plate become larger, though remaining slender and perfectly straight, 

 till in about the 27th row their ends are slightly curved outwards (cp represents the 

 central plate of the 31st row). 



* I.e. p. 22, PI. in. fig. 75. Moreover the same feature has been noted by me (p. 73) in Carinaria 

 macrorhynchus. Hedley (I.e. p. 335), however, ascribes two tentacles to Pterosoma. 

 t I.e. p. 48, PI. VI. fig. 1. 

 I This crest was not noted by Hedley (I.e. p. 335, fig. 3). 



SECOND SERIES— ZOOLOGY, VOL. XIV. 23 



