Prof. Owen's Description of the Lepidosiren annectens. 355 



want the pancreatic cseca, the analogy which Lepidosiren offers to one genus 

 in that group, Belone, in the elongated slender form of the body and its green 

 bones, is not without interest. 



In the low condition to which the pectoral and ventral fins are reduced, 

 the zoologist who deals merely with external characters would see in the 

 Lepidosiren a transitional form between the abdominal and apodal groups of 

 the Malacopterygii. But by far the most important ajffinities which a deeper 

 research into the organization of the Lepidosiren brings to light, are those to 

 the higher Cartilaginous Fishes which are indicated by the semiossified con- 

 dition of its skeleton ; by the removal of the acoustic labyrinth from the cavity 

 into the parietes of the skull ; by the number of branchial arches ; by the sim- 

 plicity of the maxillary apparatus ; by the spii'al intestinal valve ; and, above 

 all, by the condition of the oviducts as distinct tubes with two separate aper- 

 tures. 



From every group of Fishes, however, the Lepidosiren is sufficiently distinct 

 to form the type not merely of a genus, but of a family ; and, in the natural 

 system, it forms a link connecting the higher Cartilaginous Fishes with the 

 Sauroid genera Polypterus and Lepidosteus ; and at the same time makes the 

 nearest approach in the class of Fishes to the Perennibranchiate Reptiles. 



EXPLANATION OF THE PLATES. 



Tab. XXIII. 



External Form and Skeleton of the Lepidosiren annectens, on the scale of 



8 inches to a foot. 



Fig. 1 . Side view of Lepidosiren annectens. 



2. Upper view of the same, in outline. 



a. Filamentary anterior extremities, or pectoral fins. 

 b. posterior extremities, or ventral fins. 



3. Transverse section of the same, one inch in advance of the ventral 



filaments. 



