131 



differing in their size. The eyes are less prominent than those of 

 the P. plana. Between the eyes is a smooth ridge, covered by the 

 common cuticle of the head as far back as the posterior angle of 

 the orbit of the upper eye. From this point it becomes naked and 

 rough, and is continued back to the superior angle of the opercu- 

 lum, where it is much larger than at any other point, and termi- 

 nates in an obtuse point. The posterior extremities of the ventrals 

 do not reach the anal fin. The teeth are cylindrical, slightly con- 

 ical at their points. The hyoid bone has numerous blunted teeth. 

 The fin rays are D. 54, P. 9, V. 6, A. 39, C. 16. Inhabits Boston 

 harbor in company with P. plana. 



Mr. Charles H. Olmsted, of E. Hartford, Conn., present- 

 ed to the Cabinet, through Dr. Storer, specimens of the 

 Leuciscus nasutus and L. comutits, taken by him at Bland- 

 ford, Hampden Co., Mass. 



Dr. Wyman exhibited some microscopic sections of the 

 teeth of the Duck-bill Gar, (Lepidostens platyrhinus,) and 

 of L. oxyurus. He pointed out the analogies which exist 

 between the structure of the teeth of the Lepidostei and 

 those of the Labyrinthodonts, described by Prof. Owen, in 

 his Odontography. 



Like those of the Labyrinthodonts they are characterized by 

 processes of the pulp-cavity radiating towards the circumference, 

 and by prolongations of the cementum towards the centre of the 

 tooth, enclosing between them the " dentine.' 1 In the Labyrintho- 

 donts the prolongations of cementum are more or less undulating, 

 except in the L. lejjtognathus, where they present almost precisely 

 the conformation met with in the Lepidosteus oxyurus. Of the ex- 

 istence of such a structure in fishes, Prof. Owen does not appear 

 to have been aware, since he says, " such a disposition of the ex- 

 ternal substance may be traced at the base of the teeth of a few 

 fishes, but is more conspicuous in the fang of the Ichthyosaurus." 

 If the sections of the teeth of the Gars be compared with that 

 of the tooth of the Ichthyosaurus, given by Prof. Owen, it will be 

 at once seen, that the former present the same plan, but far more 

 extensively carried out. Other analogies with the Labyrinthodonts 

 17* 



