of the Fishery Board for Scotland. 301 



(2.) Arnnfliorotyle elegans, Mouticelli. This was described in 1890 

 (Boll. Soc. Napoli, iv., p. 191, fig. III.), it measures from two to four 

 millimetres in length, and, like the other, was found on the back of a 

 Thornback Skate captured in the Gulf of Naples. 



(3.) Acantlwrotyle oliyoterus, Monticelli. This species was obtained on 

 the under (ventral) side of a Thornback Skate captured in the Gulf of 

 Naples in 1893, but Avas not described till 1899, in Archives de 

 Parasitologie, II. No. i., p. 115. This appears to be the smallest of the 

 three species, as it measures only from one and a half to two and a 

 half millimetres. 



The learned author, after whom the present species is named, informs 

 me that another Amntlitcotyle — A. verrilli, Goto — is described in Journ. 

 Coll. Sc. Imp. Univ. Tokyo, 1899, p. 4; but that our species differs from 

 it as well as from the others mentioned above. 



The following are one or two of the more easily observed characters 

 which distinguish AcanthocotyJe from other Trematodes, and by which 

 also the different species of Acantlwcot ijle may be distinguished. First, 

 the structure of the posterior sucker (ventouse) differs from that of other 

 Trematodes ; this sucker is provided with numerous rows of .small teeth — 

 twenty rows appear to be the prevailing number, as this is the number 

 in the species I record (see fig. 32), and it is also the number in the three 

 species described by Monticelli. Second, the large posterior sucker is 

 provided with a minute supplementary disk — the " adhesive disk," — 

 situated at its posterior end (as shown in fig. 32). In Acanthocotyle 

 lobiancoi this disli is tongue-shaped (lingualate), but in the other three 

 species it is circular in form. In Acanthocotyle elegans the posterior 

 edge of the adhesive disk is almost in line with the posterior margin of 

 the large sucker.* In A. olii/oterus about half of the adhesive disk 

 extends beyond the margin of the sucker ; while in A. concinna the whole 

 of the disk is outside. 



The adhesive disk is armed with a number of small hooks that appear 

 to be placed at the ends of the stalk-like processes, and which in their 

 form and arrangement differ to some extent in the different species. In 

 A. lobiancoi these hooks, which appear to be eight in number, are arranged 

 along and just within the posterior margin, their stalks being directed 

 inward like the radii of a circle. In A. elegans and A. oHgoterus, the 

 number of hooks is fifteen, and they are arranged in regular order all 

 round and a little within the circumference of the disk, with their stalks 

 directed towards its centre. In A. monticellii, on the other hand, the 

 adhesive disk appears to be furnished with sixteen hooks, fourteen of 

 which are arranged somewhat irregularly around the circumference, while 

 two are sub-central ; the stalks of these hooks are not directed toward the 

 centre so regularly as in the other species. 



It may also be noted that in the species recorded here the teeth form a 

 continuous row, each being joined to the other as shown in figure 32a. 

 Acanthorotyle moriticellii appears also to be a larger species than any of 

 those described by the author referred to; the largest of the species 

 recorded by him is A. lobiancoi, which measures from three to six 

 millimetres in length, whereas the length of our specimen extends to about 

 six and a half millimetres. 



It may be of interest to state that M. Monticcelli, who very kindly 

 examined for me not only this but also several other Scottish Trematodes, 



* lu this species, the margin of the large sucker is fringed with short, narrow, and 

 somewhat irregular scallops ; and in this respect it differs from the next two species in 

 which the niarjjin of the sucker is plain. 



