Br. S. Woodicard — On the Fossil Sirenia. 421 



in size, and the neural spine is moderately large; but the transverse 

 processes are very flat, long, broad and straight, being in relation 

 to the centrum as 5 to 1. 



The centra of the caudal vertebrge are rounder, the transverse 

 processes are short and stout and bent backwards ; the neural canal 

 is reduced to a very small size, and the neural spine gradually dis- 

 appears. 



The 11th to 16th thoracic or dorsal vertebree have irregularly 

 developed hypapophyses on the ventral surface of their centra. 



There are 19 pairs of ribs in Rhytina, probably not more than 

 two pairs of which were articulated to the sternum. The 1st and 

 2nd pairs are short and much compressed laterally, the third and 

 following are round and very massive, and increase in curvature 

 and length up to the 12th, when they gradually become shorter and 

 less curved, the 19th being quite rudimentary. 



The ovoid visceral cavity thus inclosed within the bony walls of 

 the ribs is of vast dimensions ; and one realizes readily the statement 

 that a full-grown male, covered with its integument and flesh, 

 weighed as much as 3^ tons. 



This large number of rib-bearing vertebras in the Sirenia is only 

 equalled in Elephas and Rhinoceros, and only exceeded in Bendro- 

 hyrax (which has 22 costal vertebra), thus aifording an interesting 

 point of analogy in Rhytina to the Ungulata. 



Another point of comparison is observable in the teeth in Manatiis 

 and Halitherium, which have a most remarkable resemblance to the 

 molars in Hippopotamus, Mastodon, and the Suid^. 



Dr. Murie strongly insists upon the dermal characters as ofi'ering 

 a further close resemblance between Manatus and Elephas. The 

 short (rudimentary) nasal bones and the prolonged premaxillaries. 

 with their tusk-like incisors, afford additional points of resemblance 

 with the Proboscidea. 



The Sirenia pass their whole life in the water, being denizens of 

 shallow bays, estuaries, lagoons, and large rivers ; but they never 

 venture far away from the shore. Their food consists entirely 

 of aquatic plants, upon which they browse beneath the surface, as 

 the terrestrial herbivorous mammals feed upon the green pastures 

 on land. 



When Steller came to Behring's Island in 1741, the Sea-cows 

 pastured in the shallows along the shore, and collected in herds like 

 cattle. As they fed, they raised their heads every four or five 

 minutes from below water in order to breathe before again descending 

 to browse on the thick beds of sea- weed which surround the coast.^ 



1 My colleague, Mr. ■William Carruthers, F.E.S., F.G.S., Keeper of the Botanical 

 Department, informs me that the large sea-weeds called Laininarice grow in water at 

 or just below low-water ; they are nutritious and are eaten by animals. They 

 abound in the North Pacific Ocean. Ruprecht, in his account of the Algte of the 

 North Pacific, records eight species of these large weeds growing in the Sea of 

 Ochotsk, on the shores of Kamtschatka, and the north of North America. He 

 adds: — ''When I went to see the Coniferous trees at Monterey, California, last 

 autumn, I was surprised at the magnitude and quantity of the Faa and Laininanee 

 thrown up on the coast." 



