100 CEYLON PEARL OYSTER REPORT. 



on the sides of the body (in Deropristis and in Distomum semiarmatum). Uterus 

 running directly oral (in Stephanochasmu* and Acanthocolpus), or at first tail wards 

 and then turning in front of the testes (in Deropristis), or reaching the posterior end 

 of the body (in Distomum semiarmatum). Vagina always very distinct and provided 

 with similar spines to the cirrus. Genital atrium tubular, almost without spines, 

 but sometimes (in Acanthocolpus) in its posterior part with similar spines to the 

 vagina and cirrus. Genital opening in front of the ventral sucker in the median line. 

 From the generic differences mentioned in this diagnosis it results that Acantho- 

 colpus is much more closely related to Stephanocliasmus than to Deropristis and to 

 Distomum semiarmatum. 



Acanthocolpus, n. gen. 



Provisional Generic Diagnosis : Distomids of small size, with a thin, slender, very 

 elongated body, round or oval in cross-section, without spines in the skin and around 

 the mouth, with a transverse section of oval shape, rounded behind, somewhat pointed 

 in front. Neck not enlarged. Ventral sucker near the anterior end of the body some- 

 what pediculated. Oral sucker subterminal, followed by a very distinct prsepharynx. 

 Pharynx well developed, not far in front of the ventral sucker. (Esophagus short. 

 Intestinal coeca long, ending not very far in front of the posterior end of the body. 



Genital opening just before the short stalk of the ventral sucker in the median line. 

 The two testes are oval shaped, with the longest diameter in about the long axis of the 

 body, situated near the posterior end of the body in the median line, just behind each 

 other. Ovary just in front of the testes. Very numerous follicles of yolk glands on 

 the sides of the body and behind the testes, reaching the posterior end of the body. 



Uterus developed in the same manner as in Sfephanochasmus, opening into a very 

 distinct long vagina, which bears on its inner side numerous spines ; cirrus-pouch very 

 long, vesicula seminalis and pars prostatica lying on the dorsal side of the uterus ; 

 cirrus of about the same length and with similar spines to the vagina. Cirrus and 

 vagina opening into a long, tubular, genital atrium, the posterior half of which 

 bears likewise similar spines to the cirrus and vagina. The spines are of a very 

 characteristic shape, much broadened, and excavated at their bases. Eggs yellow- 

 tinted. 



This new genus, the type, and till now only species, of which is Acanthocolpus 

 liodorus, is allied to the genera Stephanochasmus, Lss., and Deropristis, ODHN., and 

 to another genus hitherto still unnamed, the type species of which is Distomum 

 semiarmatum, MOL., a parasite of the sturgeon, found by me several years ago at 

 Trieste, but the description of which I have not yet published, since another 

 helminthologist, to whom I have sent my drawings, intended to write a special report 

 upon the Trematode parasites of the sturgeon. 



The above-named genera form together a separate sub-family, which I have named 

 Acanthocolpinae, the spines in the vagina being one of the striking characters. 



