ELASMOBRANCHII 441 



There are a few differences in the digestive systems of the two. 

 In the pharynx there are no spiracles. The stomach of Reniceps is 

 J-shaped instead of U-shaped and the long slender pyloric portion is 

 armlike. The spiral folds of the spiral valve are more telescoped 

 into each other than in Squalus. There are only two lobes in the 

 liver of bonnethead and the gall bladder is nearly embedded in its 

 tissue. In the circulatory system, Reniceps has five afferent branchial 

 arteries branching from the ventral aorta while Squalus has only 

 three, two of which branch. The branching of the coeliac artery is 

 somewhat different in the two animals. 



The brain has the same general parts as it does in Squalus but 

 they are quite modified. The olfactory lobes are broader and almost 

 completely fused to each other. The cerebrum is a somewhat smaller 

 single lobe just posterior and dorsal to the olfactory lobes. There 

 is no line of demarcation between the hemispheres. The diencepha- 

 lon is entirely hidden from dorsal view by the cerebrum and cere- 

 bellum. The latter is large, irregularly divided into three lobes, and 

 convoluted. It covers not only the diencephalon but also most of 

 the optic lobes (midbrain) and much of the medulla oblongata. The 

 medulla has well-developed acousticolateral areas. 



The nasal chambers of Reniceps are quite large and kidney-shaped. 

 They contain extensive folds or lamellae of the olfactory membrane. 



The shape of the testes in male Reniceps is much longer and more 

 slender than in Squalus. In addition to this, there is a long glandu- 

 lar body, the epigonad, which extends from the level of the gonad 

 proper to the region of the cloaca. 



Copulation in Reniceps probably occurs during May and June in 

 the Gulf of Mexico, at the time when they are so numerous in the 

 shore waters. Fairly mature "pups," ^s the developing young are 

 called, have been found in the uteri of specimens collected off shore 

 in Texas Gulf waters in late August and early September. 



