1184 



SCANDIXAVIAX l-ISIIKS. 



ellii)tie;il disk. la its tirst-iiiuiitiuiicd coiiditiuii, when 

 the disk can almost be folded together from the sides, 

 its length is al)out equal to the deptii uf the body, 

 somewhat greater or less, and as a nile more tlian * ,, 

 of the length of the snout (to the anterior margin of 

 the eyes), which varies between 10° and 8 % (excep- 

 tionally approaching 7 %) of the length of tlie body 

 or between "//' -"kI 7.i "^ ^1'''^ "^ ^'i'' 'i^-ad to the first 

 gill-opening. 



In the mere size of this suctorial disk, even rela- 

 tivel)- greater than in the following forms, we have a 



est 



medinn line), directed in a niore or less sharp crook 

 towards tiie mouth; but exactly in tiie ])reoral median 

 line tiic row is straight, and the rows on the posterior 

 part of the suctorial disk are only slightly curved, each 

 row being dii'ected in\vards with fair rcgularit}' towards 

 one of the teeth (cusps) of the posterior dental plate 

 of the mouth. The teeth in these rows (the suctorial 

 teetli, tig. 352, est and 'ist) are unicuspidate, conical, 

 gradually increasiiig in size inwards, separated by 

 grooves in the gums, which are thus divided into lo- 

 zenges, one to each tooth. Four rows meet the sides 







nln- 



Fig. 352. Oral disk of a Lauiprt-y (Petroiiii/:on manmin) 8'/,, cm. long, X 2. 



ahi, aiilorior lingiiodental plate; fill, anterior lateral dental plate; at, anterior dental plate; esl. onter suctorial teeth; w^ inner suctorial teeth 



mil, niediolateral dental ]ilate; jilii, posterior linguodental plate; j'll, posteri<.r lateral dental plate; pt, posterior dental plate. 



of the mouth, and the two innermost (largest) teeth in 

 these rows (the lateral teeth, aJt, niU, and pit) are so 

 closely set that they are joined at the ba.se into liicuspid 

 teeth, eacli on its o^vn root (lateral dental plate). The 

 fringes (dermal papillre), and within these appear nu- ' iMcuspid anterior dental plate of the mouth {at), situated 

 merous rows of teeth (12 or 11 on each side of the \ between but a little behind the anterior lateral plates. 



very good character for tiie Sea Lamprey; but tiie most 

 characteristic peculiarities are shown by the dentition 

 of the moutii and tongue. Tiie suctorial disk is edged 

 witli a (hiuble or multifarious series of densely .set 



" Sometimes 11 in the variety occurring in Cayuga Lake (at Ithaca, N, Y.); see Meek in Jordan and Foupice, 1. c. 

 ' In exceptional cases only 63 '/<,; see Meek. 1. c. 



