85 



Order IX. PROTOPTERI. 



Family SirentAe. 



The skeleton of the African Lcpidosiren (Protopteru* annecfem, Owen). 



The chief peculiarities of thin skeleton consist in it* imperfect, or rather partial ossification, 

 and in the green colour of thr ossified part*, in which latter respect it resembles the Hrlonr 

 rulgaru. The parts which continue |>ermanently in the cartilaginous condition are the petrous 

 rlemriits of the temporal, containing the auditory vestibule* ; the branchial arches ; and the 

 bodies of the vertebra: : these, moreover, are not separated to correspond with the pairs of 

 neuwpophyses and ribs, as in the Plagioxtomous Cartilaginous Fishes, but retain, as in the 

 Lampreys, their primitive confluent condition as a round continuous chord, extending from 

 the occiput to the end of the tail. This chord consisU of an external, firm, elastic yellowish 

 capsule, enveloping a softer subgelatinous material, a* in the Sturgeon and Cyclostomous 

 Fuh. 



The ribs are 36 pairs, in the form of short, slightly -curved, or straight and slender style* . 

 encompassing, with the spine, about one-sixth part of the cavity of the abdomen. Thrw 

 ribs are attached to the lower part of the side of the fibrous sheath of the central vertebral 

 chord ; their pointed free extremities are connected to the intermuscular fasciae. 



The neural spines are throughout separate from the neurapophyses ; and these, at the 

 anterior and posterior regions of the spinal column, are not anchylosed together at their upper 

 extremities. Haemal spines are developed in the caudal region, and both these and the neural 

 spines have articulated to them dermal osseous spines, of equal length, with their distal ex- 

 tremities expanded. 



The rudimental filiform fins were supported each by a cartilaginous ray composed of many 

 joints. 



The Protoptmtt annfrttnt manifests an additional important evidence of its essentially 

 ichthyic nature, by having its scapular arch directly suspended to the skull, but with this 

 peculiarity, that it is connected by a synovia! joint with the exoccipitals only. 



In all osseous fishes, and in those Ganoids, as the Sturgeons, r. g., that come nearest to 

 the Lepidosiren in some parts of their structure, the scapula is suspended by two processes 

 to the paroccipital and to the mastoid. 



The Plagiostomous Cartilaginous Fishes on the other hand have no cranial point of sus- 

 pension for the scapular arch, and in the Shark-tribe the arch has no fixed point at all. 



Hab. The Gambia river. 



Prepared from a specimen presented by Thomas Weir, Esq. 



381. The partly osseous, partly cartilaginous skull of the African Lepidosiren (Pro- 

 topterux annecteiu). 



With regard to the vertebral bodies, ossification is limited to the cranial end of the noto- 

 chonl, and there extends along the under and lateral part of its sheath forwards to the pi*- 



