SCIENTIFIC SURVEY. 57 



connected by a commissure, but do not cross each other. The bul- 

 bus arteriosus or aorta has a thick muscular coat, and is provided 

 with at least two rows of semi-lunar valves. The intestine has a 

 spiral valve. The males are provided with the so called " claspers," 

 which are present as appendages to the posterior edge of the ven- 

 tral fins. Fecundation is effected by copulation. The branchial 

 apertures are usually five in number, and are generally aZ^ external. 

 There is no air bladder. 



This sub-class was divided into two orders, viz : Plagiostomi, 

 (oblique mouths,) and Ilolocephali, (solid heads.) The Plagios- 

 tomi are distinguished by several separate branchial apertures on 

 the side of the neck, and the Holocephali with only one branchial 

 aperture on each side, as in the true fishes. The Plagiostomi order 

 was divided into four sub-orders, viz : Squali, Rhinae, Pristes and 

 Raiae ; and this arrangement is so laid down in Prof. Gill's cata- 

 logue of East Coast fishes before referred to. Subsequently, 

 further investigation of the Sharks and Rays, has induced the Pro- 

 fessor to modify this arrangement by raising the Squali to a full 

 order, dividing it into several families and sub-families, and reserv- 

 ing the Rhinae and Raiai (Rays) as sub-orders. The divisions, 

 therefore, of this sub-class, (Elasmobranchii,) are 



Order Squali ; Gill. 



Several branchial apertures on the side of the neck, — pre-supple- 

 mentary eye-lids. An incomplete scapular arch ; naso-pectoral 

 cartilage absent. 



Sub-order Rhinae ; Gill. 



This sub-order is distinguished from the Squali by the depressed 

 head and body, and the dorsal position of the eyes. The branchial 

 apertures are situated on the sides, but are placed in a fur-row 

 which separates the large expanded pectoral fins from the body. 

 The mouth is at the extremity of the snout. 



SuB-oRDER Rai^e ; Mullev & Eenle. 



The RaicB have the branchial apertures beneath the body under 

 the pectoral fins. The body is flattened until from its union with 

 the large and fleshy pectorals it forms a disc. These pectorals are 

 united before the snout. Eyes and spout holes are always above 



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