glossary/ 387 



HoMOCERCAL (Gr. homos, same ; kerkos, tail). Applied to the tail of Fishes 

 when it is symmetrical, or composed of two equal lobes. 



Hybodonts (Gr. hubos, curved ; odous, tooth). A group of Fishes of which 

 Uybodus is the type-genus. 



Hydroida (Gr. hndra ; and eidos, form). The sub-class of the Hydroz&a, 

 which comprises the animals most nearly allied to the Hydra. 



Hydrozoa (Gr. hudra ; and zoon, animal). The class of the CteZew^erato which 

 compiises animals constructed after the type of the Hydra. 



Hymenoptera (Gr. hitmen, a membrane; pteron, awing). An order of In- 

 sects (comprising Bees, Ants, &c.) characterised by the possession of four 

 membranous wings. 



ICHTHYODORULITE (Gr. ichthus, fish ; dorus, spear ; lithos, stone). The fossil 



fin-spine of Fishes. 

 IcHTHYOPTERYGiA (Gr. ichthus ; pterux, wing). An extinct order of Reptiles. 

 ICHTHYORNis (Gr. ichthus, fish ; ornis, bird). An extinct genus of Birds. 

 IcHTHYOSAURiA (Gr. ichthus J saura, lizard). Synonymous with Ichthyop- 



terygia. 

 Iguanodon {Iguana, a living lizard ; Gr. odous, tooth). A genus of Deinosau- 



rian Reptiles. 

 Incisor (Lat. incido, I cut). The cutting teeth fixed in the intermaxillary 



bones of the Mammalm, and the corresponding teeth in the lower jaw. 

 Inequilateral. Having the two sides unequal, as in the case of the shells of 



the ordinary bivalves {Lamellibranchiata) . When applied to the shells of 



the Foraviinifera, it implies that the convolutions of the shell do not lie in 



the same plane, but are obliquely wound round an axis. 

 Inequivalve, Composed of two unequal pieces or valves. 

 Inoceramus (Gr. is, a fibre ; keramos, an earthen vessel). An extinct genus of 



Bivalve Molluscs. 

 Insecta (Lat. inseco, I cut into). The class of articulate animals commonly 



known as Insects. 

 Insectlv^ORA (Lat. insectum, an insect ; voro, I devour). An order of Mammals. 

 Insectivorous. Living upon Insects. 

 Insessores (Lat. insedeo, I sit upon). The order of the Perching Birds, often 



called Passeres. 

 Interambulacra. The rows of plates in an Echinoid which are not per- 

 forated for the emission of the " tube-feet." 

 iNTERiSLiXiLL^ Or Pr^maxill^. The two bones which are situated between 



the two superior maxillae in Vertehrata. In man, and some monkeys, the 



praemaxillae anchylose with the maxillae, so as to be irrecognisable in the 



adult. 

 Invertebrata (Lat. in, without ; vertebra, a bone of the back). Animals 



without a spinal column or backbone. 

 IsoPODA (Gr. isos, equal ; podes, feet). An order of Crustacea in which the 



feet are like one another and equal. 



Kainozoic (Gr. kainos, recent ; zoe, life). The Tertiary period in Geology 

 comprising those formations in which the organic remains approximate 

 more or less closely to the existing fauna and flora. 



Labyrinthodontia (Gr. lahurinthos, a labyrinth ; odous, tooth). An extinct 

 order of Amphibia, so called from the complex microscopic structure of the 

 teeth. 



LACERTfLiA (Lat. lacerta, a lizard). An order of Reptilia comprising the Liz- 

 ards and Slow-worms. 



Lamellibranchiata (Lat. lamella, a plate ; Gr. bragchia, gill). The class of 

 Mollusca comprising the ordinary bivalves, characterised by the possession 

 of lamellar gills. 



Lepidodendron (Gr. Upis, a scale ; dendron, a tree). A genus of extinct plants, 

 so named from the scale-like scars upon the stem left by the falling off" of the 

 leaves. 



