SKA LAMl'REY. 



US') 



is ot .•ilioiit tlie same size us these and of the saiiio 

 t'orm. 'I'Ik' crescent-shaped posterior dental plafc <it' the 

 nioiitli (jif). on the otiiei- hand, is coiisiderahly hii'ger. 

 In yoiniii' s]ii'ciinens it is comparatively hiu'lier than in 

 old, hnt also has coniparativch' smaller ami usually 

 more inimerous (in ma!iy cases 8") and more pointed 

 teeth. In old si)eciinens the latter (usually 7) are more 

 conical, ol' alxiut the same si/.(^ and t'onii as the large 

 lateral tct'th. All these teeth proliahh' serve merely as 

 an adhesive oi-gan that holds the Lamprey fast to the 

 skin of its pre\', which is forced to drag it along. 

 Withiti the month is the rasping lingual appai-atus that 

 opens the skin of the \ictim and saws into its flesh. 

 The anterior linguodental plate (lingual ])late, nlii) is 

 indeed simple and curved semilunarly like the posterior 

 dental plate of the month; but at the middle it is dee])ly 

 recurved, thus acquiring the form of a S. Of the two 

 loojis thus ]iroduced the left bears 7 or ti, the right (i 

 or .i sharp points (tooth-cusps), exclusive of the hind- 

 most median tooth of the plate. Here too it seems to 

 be the ride that young Lampreys have more numerous 

 and more |)ointed teeth than old*. Behind (within) this 

 plate lie the posterior linguodental plates (supi'alingual 

 plates, pin) beside one another, each resembling in form 

 a reversed ruminant hoof, with the crook directed for- 

 wards and parallel to one of the loops of the anterioi' 

 linguodental ]ilate. The left supralingual ]date is usually 

 furnished with I -H jiointed teeth, the right with 12, 

 these being largest in front, on the crook, gradually 

 smaller behind. 



The eyes are rounil. Tlieii' size varies considerably 

 with age; but as they arc; covered by the more or less 

 transparent skin, the measurements taken depend greatly 

 on the traiis|iarencv of the skin and the method of 

 measuring. In Sea Lanijireys 4 — 8' , dm. long Kkover 

 found the diameter of the eves to be ^ ^ % of the length 

 of the body or about 7 % of the length of tlie head to 

 the first gill-o])ening. Our measurements of the outer 

 diameter of the iris in so large specimens fix the latter 



percentage at about lU or ij'. The opening of the 

 nasal duct (the nostril), more or less distinctly ele- 

 vated into a tul)e, is about ' ,, as large as the eyes, 

 and is situated just in front of the interoi'bital space, 

 at a distance from the tip of the snout measuring about 

 -' ., ((i?,— 7(» ",.) of the said length of the head. Behind 

 the nasal duct lies the light, elliptical, but indis- 

 tinctly bounded epiphj'seal spot. 



The gill-openings are comparatively small (see our 

 i\<!:\{n- in I'l. LllI), but when distended they attain a 

 height not uuicli less than the diametcn- of the eyes. 

 Th(!y -An- each coNci-ed IVom ill front, partly by the 

 anterior margin itself, which forms a vertical dermal 

 fla]). partly by t\vo other, somewhat pateriforni, rounded 

 dermal lobes, one of which rises from the inn<r part 

 of the lower wall of the gill-opening, the other hanging 

 down in a similar maimer from a])ove. The hind mar- 

 gin of each gill-oi)ening is furnished with small fi-inges 

 and jjapilbv. The total extent occupied by the seven 

 gill-opeiiings in a row one after another measures about 

 9 or 10 "-■/ of the length of the bod}', and in young 

 Sea Lampreys ('2 — >> dm. long) is in many cases equal 

 to the length of the snout to the nostril or about ^/^ 

 of the length of the head to the first gill-opening'', in 

 the old greater, about Vr, (77—84 %) of the said length 

 of tlie head, wiiich in the young is up to 1.5 %, in the 

 old only about 11 %, of the length of the body. 



'i'he first dorsal fin is an elongated, low triangle, 

 with the greatest depth ('4 — '/< <>f" fh« length) situated 

 in the anterior part, but with the anterior end indis- 

 tinctly delimited from the dorsal edge of the body, 

 which margin in i'i|)e individuals (oftenest in males, 

 but sometimes too in females) may rise into a. hard 

 carina both before the first dorsal fin and between it 

 and the second dorsal. This renders it also ditfictdt 

 to determine with certainty tile distance between the 

 first d<5rsal and the tiji of the snout', but the rule 

 appears to be that the fin commences close behind or 

 even at the middle of the body, comparatively further 



" According to Meek (I. c.) exceptionally 9. 



' Bluuter and sli.irper tcctli thus occur in this species as in the following oue. In cstininling tlio ini|iiirtiiuci' of tliis dift'erencc, which 



is by no means exclusively dependent on age, it should be remembered that we have liere to deal not witli real teetli, but only with points 



of homy sheaths, which are changed time after time. In ordinary cases the homy sheath is so loosely attached to the plate that it can be 

 removed altogether, new, unworn, and tliereforc (if they lie fidly developed) more pointed teeth being thus exposed to view. 



"" LiLLJEBORG gives 9 or S «, (' j, — ' lo)- .\ccording In Meek (1. r.) tliis percentage is about 16 — 1.3 in Sea Lampreys 2' ^ — 3' j 



dm. long from Cayuga Lake. 



'' .\ccording to Meek (1. c.) sometimes only 5.5 % of the last-mentioned lengtli. 



' According to Meek tliis ilistance v.iries witli great irregularity between 55' 2 ""'l 49 % of the length of the body. 



