Prof. Owen on the Lepidosiren annectens. 75 



them without forming any projection ; they have a small spherical 

 lens, and no choroid gland. 



The organ of hearing consists of a vestibule enclosed in a thick 

 cartilaginous case, without external communication except for the 

 foramina transmitting the portio mollis : it consists of two large 

 otolithic sacs, containing each a white chalky mass ; the external one 

 being six times the size of the one next the brain : above these sacs 

 are three small semicircular canals. No trace of tympanic cavity or 

 Eustachian tube. 



The organ of smell consists of two oval membranous sacs, pli- 

 cated internally, and having each a single external aperture upon 

 the upper lip ; but without any communication with the mouth, — a 

 structure which the author observed was perhaps the only single 

 character which unexceptionably proved the Lepidosiren to be a true 

 fish. The remaining evidence of its ichthyic nature reposed rather 

 upon the concurrence of many less decisive characters. 



These characters were stated to be, its covering of large round 

 scales ; the mucous ducts of the head and lateral line ; the many- 

 jointed soft ray supporting the rudimental pectoral and ventral fins ; 

 the gelatinous vertebral chord, united anteriorly to the whole of the 

 basi- occipital, and not to two condyles as in Batrachia ; a prse- 

 opercular bone, the intermaxillary bone being moveable ; the lower 

 jaw having each ramus composed simply of a post-mandibular and 

 dentary piece ; the double row of spinous processes, both above and 

 below the vertebral chord ; the green colour of the ossified parts of 

 the skeleton ; the straight intestine, with its spiral valve ; the absence 

 of pancreas and spleen ; the single peritoneal outlet ; the position 

 of the anus ; the single auricle of the heart ; the number of branchial 

 arches, and the internal position of the gills ; a long lateral nerve ; 

 acoustic labyrinth with large otolithes. These characters, with the 

 nasal sacs opening only externally, prove satisfactorily the Lepido- 

 siren to be a true Fish, and not a Perennibranchiate Reptile. 



In the class of fishes, Mr. Owen pointed out the interesting rela- 

 tions of the Lepidosiren as a link connecting the Cartilaginous fishes 

 with the Malacopterygians, and especially with the Sauroid genera, 

 Polypterus and Lepidosteus, and at the same time making the near- 

 est approach in the class of fishes to the Perennibranchiate Reptiles. 



For the species here described Mr. Owen proposed the name of 

 Lepidosiren annectens. It is a native of the river Gambia, Africa. 



FRIDAY-EVENING MEETINGS AT THE ROYAL INSTITUTION. 



April 12th. — Mr. Everitt on Professor Liebig's method of analy- 

 sing organic bodies. 



April 19. — Mr. Cottam on the manufacture of bricks and draining 

 tiles by machinery. 



April 26th. — Mr. J. T. Cooper on his instrument for measuring 

 altitudes, the baroscope. 



May 3. — Mr. S. Solly on the structure of birds in relation to 

 their habits of life and position in the animal kingdom. 



May 10. — Mr. Faraday. Some general remarks on flame. 



