i85 

 PLANER'S LAMPREY NEAR SCARBOROUGH. 



W. J. CLARKE, F.Z.S., 



Scarborough. 



During the latter half of -April a considerable migration of 

 this interesting little fish has taken place in the waters of the 

 Upper Derwent at Forge Valley and Hackness, near Scar- 

 borough. On April 15th, numbers of them could be seen 

 swimming up sti'eam near the surface of the water, and others 

 were observed on the i6th, 19th, 23rd, 24th, and 29th ; after 

 which date, only a single specimen was noticed. All the indi- 

 viduals captured were adults, probably making their way up 

 stream for the purpose of depositing their spawn. The usual 

 length was about five and a half to six inches, very few exceeding 

 the latter size. Lampetra planeri may be distinguished from 

 its larger relative the River Lamprey {Lampetra fluviatilis) by 

 the close contact of the first and second dorsal fins, which are 

 separated in the larger species, and also by the presence on 

 the circular lip of numerous papillae, from which it has taken 

 the name of Fringe-lipped Lamprey. Specimens from the south 

 reach a length of eight or nine inches, the females being a little 

 larger than the males ; but northern examples do not usually 

 €xceed six inches. The Lampreys are remarkable for under- 

 going a metamorphosis from a larval form to the adult stage, 

 which has been carefully worked out in the case of Planer's 

 Lamprey. In the larval state, which takes three years to 

 complete, the sucking disc is imperfect, and has not the power 

 ■of adhesion found in the adult. 



The eyes are very small, and almost hidden in a fold on 

 the skin ; there are no teeth ; and there are important intestinal 

 differences. In the fourth year the change to the perfect form 

 takes place, and occupies about ten days. There is no increase 

 in size, but rather the reverse, the perfect form being smaller 

 than the larva owing to the shortening of the intestinal canal. 

 At this time a separate respiratory tube is acquired, teeth 

 appear, the eyes are much 'enlarged, and the lips are formed 

 into a complete sucking disc. The larva, not having the power 

 of clinging to stones like the adult, lives buried in the mud at 

 the bottom of the stream, and has been described as a distinct 

 species under the names of Mud Lurker, Mud Lamprey, Sand 

 Pride, and Pride. It is described under this name in the 

 ■* Vertebrate Fauna of Yorkshire ' as occurring in the rivers of 

 our county, but 'no mention is made of the adult form. 



I noticed an example quietly swimming up stream a few 

 inches from the bank where the current was not so strong, 

 when a trout made a dash at it, but missed. The frightened 

 fish darted to the bank and threw itself out of the water. The 

 trout, disappointed of its prey, after cruising about for a few 

 moments, left the place ; but the lamprey lay upon the moist 

 earth for probably ten minutes before it re-entered the water 

 and continued its journey up stream. 



3912 Jane i. 



