ELASMOBRANCHII 



439 



the funnellike ostium of the oviduct, which is held by the falciform 

 mesentery at the anterior end of the peritoneal cavity. As the ova 

 pass down the oviduct, they receive a covering which is secreted bj'' 

 the shell gland in the wall of the duct. Fertilization occurs in the 

 oviduct and the embryo develops in the uterus which is the expanded 

 lower portion of the oviduct. The embryo is nourished by the large 

 yolk mass of the egg. 



THE BONNETHEAD SHARK, RENICEPS (SPHYRNA) TIBURO 



COMPARED TO SQUALUS 



The bonnethead (or shovel-nosed) shark is common in the At- 

 lantic along the coast of the Southern States and in the Gulf of 

 Mexico. It occurs abundantly along the Louisiana and Texas Gulf 

 coast during May and June. It averages about the same size as 

 Squalus. In many respects it is similar to the smooth dogfish, 

 Mustelus canis, and the ground shark, Carcharhinns. 



Epiphyseal foramen 



M 



,. Anterior fontanel/e 





m^''"m^ .,..-|-°'^°^torycap5a/e 



^^^^ 



Supraorbital process 



-Preorbital process 

 - PosbDrbitcil process 



• Endolymphatic fossa 



Foramen maqnum' 



Endolymph i 



Fig. 238. — Dorsal view of the skull of bonnet-head shark. (From dissections by 



Mary Fickling.) 



The peculiar shovel-shaped head with the eyes out on the lateral 

 margins is one of the striking features of Reniceps by which it dif- 

 fers from the others mentioned. In Reniceps there are no spines in 

 front of the dorsal fins and a single anal fin is present on the ventral 

 side between the anus and tail. The spiracle is absent, leaving only 

 the five pairs of gill slits. The other external features are similar 

 to those of Squalus. 



The skeleton of the skull is shaped considerably different from that 

 of Squalus. This is brought about by lateral extension. Each olfac- 



