34 TREMATODES OF THE NORTHUMBERLAND COAST 



As to Cercaria strigata being the young of Gymnophallus 

 somatericB, it appears to me to differ in many respects, although 

 as Giard points out, it at the same time agrees with it in many 

 ways. For instance the length of the cercaria is almost 

 identical — in my specimens smaller, which of course is usual in 

 the larval stage. The relative size of the suckers is also 

 almost the same. Again, the arrangement of the testes is the 

 same, but this varies little in all the species of the genus. On 

 the other hand, in my specimens the cercaria is broader than 

 G. somatericE, and the striation is much more conspicuous. 

 The excretory vesicle is curved much more elaborately, and 

 is very definite and constant in its shape ; and the lobes of 

 the intestine, which are exceedingly broad, reach to below the 

 anterior margin of the ventral sucker. Finally, ducks feed 

 seldom at Alnmouth, and the occurrence of the cercaria so 

 frequently in Tellina tenuis would seem to point to a commoner 

 bird for the final host, such as one of the gulls, many of 

 which are constant feeders on the beach. Several gulls are 

 known to harbour species of Gymnophallus, e.g. G. deliciosus 

 (Olss.) in Lams argentatus, L.fitscus and L. canus. 



This cercaria occurred in every specimen of Tellina temtis 

 examined (about twenty), and it was only once found in Donax 

 vittatus out of about a dozen examined. 



Genus SPELOTREMA, Jagerskiold. 



Cercaria corophii, nov. (Plate I. fig. 4, 5.) This cercaria 

 occurs in large numbers encysted near the surface of the body 

 and legs of the Amphipods CoTOphium grossipes and Gamviarus 

 duebeni, especially in the former, just beneath the cuticle. It 

 is enclosed in cysts slightly longer than broad, measuring 

 o*i6 X c 1 4 mm., and having thick transparent walls. Within 

 the cercaria is curled up, its oral sucker and part of its 

 digestive system usually visible, and- sometimes the ventral 

 sucker. When pressed out of the cyst the cercaria is long 

 and rather narrow, the head end being smaller than the 

 posterior; length 0*34 mm., oral sucker 0-03 mm. across, 

 narrow prepharynx 0*04 mm. long, pharynx 0.016 mm. long. 



