28 Linriean Society. [April 2, 



or rudimental condition of the fins indicative of a transition from the 

 abdominal to the apodal families. 



The anatomical details which formed the principal part of the pre- 

 sent communication, confirmed the propriety of referring the Lepi- 

 dosiren to the class of fishes ; but they also led, Mr. Owen observed, 

 to a considerable extension in his original views of its affinities in 

 that class. 



A minute description was then given of the external characters 

 and peculiarities of the present species, which differed from the Le- 

 pidosiren paradox a in the greater relative length of the head and ru- 

 dimental fins as compared with that of the trunk ; and in its general 

 size, which is three-fourths smaller. 



The chief peculiarities of the skeleton consist in its imperfect, or 

 rather partial ossification, and in the green colour of the ossified 

 paits ; in which it resembles that of the gar-pike (Belone vulgaris) . 

 The parts which continue permanently in the cartilaginous condition 

 are the petrous elements of the temporal bones containing the acoustic 

 labyrinth, a portion of the articular pedicle of the lower jaw, the 

 branchial arches, and the bodies of the vertebrae : these, moreover, are 

 not separated to correspond with the neurapophyses and ribs, as in 

 Plagiostomous Cartilaginous Fishes, but retain their primitive con- 

 fluent condition as around continuous chord, extending from the oc- 

 ciput to the end of the tail : this vertebral chord consists of an ex- 

 ternal firm, elastic, yellowish capsule, enveloping a softer subgelati- 

 nous material, as in the Cyclostomous Fishes. The corresponding 

 parts or basilar elements of the cranial vertebrae were ossified : and 

 Mr. Owen then entered upon a detailed description of the skull. 



The ribs are thirty-six pairs, and consist of short, slightly curved, 

 slender styles, encompassing, with the spine, about one-sixth part of 

 the cavity of the abdomen. These ribs are attached to the lower part 

 of the side of the fibrous sheath of the central vertebral chord ; their 

 pointed free extremities are cemented to the intermuscular ligaments. 

 The superior spines are throughout separated from the neurapo- 

 physes, and these are not anchylosed together at their upper extre- 

 mities. Haemapophyseal spines are developed in the caudal region, 

 and both these and the neurapophyseal spines have articulated to 

 them dermo-osseous spines, of equal length, with their distal extre- 

 mities expanded, and supporting the transparent elastic horny raj^s 

 of the caudal fin. The rudimental filiform pectoral and ventral 

 fins were supported each by a single cartilaginous ray composed of 

 many joints. 



The muscles of the head, jaws, hyoid and branchial apparatus 



