27 



heart-shaped scute with a granular and reticulate external surface. A bony 

 ring U formed at its |Mt<nr part, which passes through a perforation in the 

 l>a.-i of the spine; which base reciprocally traverses the interneural ring, so 

 that the spine and plate are locked together like the links of a chain. The 

 spine is grooved and den tat ed posteriorly. 



Presented by William Chamber*, Esq. 



?!..'>',. !- \*> ; i 



79. The corresponding parts of a smaller Siluroid. Huiterian. 



SO. The dcrmoncural spine and articular part of the interneural plate of a Siluroid , 

 showing the linked articulation of the two parts : the base of the spine is con- 

 vex at the middle, and plays in a corresponding concavity of the interneural 

 plate ; its sides expand into two flattened surfaces which rest in corresponding 

 surfaces of the interneural plate. Hunferia*. 



81. A dennoneural osseous serrated spine of a Siluroid. Hunt man. 



82. The right coracoid bone with the anchyloscd radius and ulna, and the first ray 



of the pectoral fin of the Silum congen*i. This ray is completely ossified, 

 thick, and strong: serrated on its anterior and posterior borders. Its ex- 

 panded base is articulated by a double, interlocking, oblique trochlea. The 

 movements of flexion and extension can only be performed when the spine is 

 maintained by muscular action in a certain oblique position; any direct 

 attempt to bend back the spine, when it is at any stage of the erection, is 

 opposed by the nature of the joint. Presented by Dr. Leach, F.L.S. 



83. The corresponding bones of the left side of the same fish. The expanded inferior 



border of the coracoid is deeply notched or indented, and U articulated with 

 the opposite coracoid by suture. Presented by Dr. Leach, F.L.S. 



84. The right coracoid bone of another species of Siluroid; showing larger and 



deeper notches at the lower sutural margin of the bone. llunterian. 



85. Serrated spine* of the pectoral fins of a Siluroid. Mm. Brit. 



