72 NATURAL SCIENCE. July. 



compared with the skull of an adult collected at the Cape of Good 

 Hope. The minute structure of the teeth, both in the young and 

 adult cranium, is specially examined and compared with that of the 

 teeth in Sowerby's Whale. It is proved that, in the earlier stages of 

 growth of the teeth in these Cetacea, the structure does not differ 

 materially from the ordinary human or carnivorous tooth, the crown 

 being invested by enamel, the fang by cement, whilst the great body 

 of the tooth consists of dentine, in the core of which is a pulp-cavity. 

 The exceptional character of the erupted teeth in the adult is due to 

 the disappearance of the enamel from the crown, the cessation in the 

 development of the dentine, the excessive formation of osteo-dentine, 

 modified vaso-dentine and cement, through which the pulp-cavity 

 becomes almost obliterated, and the fang assumes dimensions, which, 

 in Layard's Whale, lead to the growth of the very remarkable strap- 

 like tooth so characteristic of this cetacean. 



The memoir also contains an account of a skull of a Ziphius 

 cavirostris (Cuvier's Whale), from New Zealand, which is compared 

 with a similar skull from the Shetland Islands. The author considers 

 them to be of the same species, and regards the geographical distribu- 

 tion of Cuvier's Whale as equal to that possessed by the Sperm 

 Whale. 



In another chapter, the cetacean bones dredged from the floor of 

 the ocean are described. These consisted mainly of the tympanic 

 and petrous bones, more or less encrusted with manganese. They 

 were all found south of the equator, and to a large extent belonged to 

 the genus Mesoplodon, of the Ziphioid group of whales, though a few 

 could not be referred to existing species. They were associated with 

 large numbers of sharks' teeth, belonging to the genera Lamna, 

 Oxyvhina, Carchayodon, but the species, so far as we know are extinct. 

 Many of the specimens were dredged from a depth of from 2,000 to 

 3,000 fathoms (PI. iii.. Fig. 3, and PL xvi., Fig. i). 



The memoir on the Seals collected by the "Challenger" contains 

 a description of the external characters and skeleton of the Elephant 

 Seal, Macrorhinus leoninus, from Kerguelen Island ; of the skeleton of 

 Weddell's Seal, Leptonychotes weddelli, from Kerguelen, a comparison 

 of the skull of a young and adult Lion Seal, Otavia jnhata, and an 

 account of the skeletons of Fur Seals collected on Kerguelen Island 

 and in the Messier Channel off the west coast of South America. 

 These latter specimens are referred to the genus ArctocepJiahs, sp. 

 gazella, australis. 



In another chapter the known species of seals and the walrus are 

 classified according to their anatomical characters, based principally 

 on a study of the skull. The distinguishing cranial characters of 

 each species are believed to be worked out with more precision than 

 in previous attempts at the classification of this interesting group of 

 marine mammals. The author does not consider that there is 

 sufficient anatomical evidence to warrant the division of the genus 



