GLOSSARY. 485 



Decapoda (Gr. dcha, ten; podcs, feet). The division of Crustacea -u'liich have 



ten ambulatory feet ; also the family of Cuttle-fishes, in which there are 



ten arms or cephalic processes. 

 Deciditoxjs (Lat. dccido, I fall off). Applied to parts which fall off or are 



shed during the life of the animal. 

 Decollated (Lat. decollo, I behead). Applied to iinivalve shells, the apex of 



which falls off in the course of growth. 

 Deinosaxjria (Gr. deinos, terrible j saura, lizard). An extinct order of Rep- 

 tiles. 

 Dendriform, Dexdritic, Dendroid (Gr. dendron, a tree). Branched like a 



tree, arborescent. 

 Dermal (Gr. derma, skin). Belonging to the integument. 

 Desmidi^. Minute fresh-water plants, of a green colour, without a siliceous 



epidermis. 

 Dexteal (Lat. dextra, the right hand). Right-handed. Applied to the 



direction of the spiral in the greater number of univalve shells. 

 Diaphragm (Gr. diaphragma, a partition). The "midriff" or the muscle 



which in Mam^nalia forms a partition between the cavities of the thorax 



and abdomen. 

 Diastema (Gr. dia, apart ; histcmi, I place). A gap or interval, especially 



between teeth. 

 DiATOMACE^ (Gr. diatemno, I sever). An order of minute plants, which are 



provided with siliceous envelopes. 

 DiBEANCHiATA (Gr. dis, twice; hragcMa, gill). The order of Cejjlialopoda 



(comprising the Cuttle-fishes, &c.) in which only two gills are present. 

 DiCTNODONTiA (Gr. dis, twice ; huon, dog ; odous, tooth). An extinct order 



of Reptiles. 

 Didelphia (Gr. dis, twice ; delphus, womb). The subdivision of Mammals 



comprising the Marsupials. 

 Digit (Lat. digitus, a finger). A finger or toe. 



DiGiTiGRADA (Lat. digitus ; gradior, I walk). A subdivision of the C'arnivora. 

 Digitigrade. Walking upon the tips of the toes, and not upon the soles of 



the feet. 

 DiMYART (Gr. dis, twice ; muon, muscle). Applied to those bivalve Mol- 

 luscs {Lamellibranchiata) in which the shell is closed by two adductor 



muscles. 

 DiNiCHTHYS (Gr. deinos, terrible ; iehthus, fish). An extinct genus of Fishes. 

 DiNOCERAS (Gr. deinos, terrible ; kercts, horn). An extinct genus of Mammals. 

 DiNOPHis (Gr. deinos, terrible ; ojjMs, snake). An extinct genus of Snakes. 

 DiNORNis (Gr. deinos, terrible ; ornis, bird). An extinct genus of Birds. 

 DiPHYODONT (Gr. dis, twice ; pJiuo, I generate ; odoios, tooth). Applied to 



those Mammals which have two sets of teeth. 

 Dipnoi (Gr. dis, twice ; pnoe, breath). The order of Fishes represented by 



the Lepidosircn. 

 DiPTERA (Gr. dis, twice ; piteron, wing). An order of Insects characterised by 



the possession of two wings. 

 Discoid (Gr. diskos, a quoit ; eidos, form). Shaped like a round plate or 



quoit. 

 DiscoPHORA (Gr. diskos, a quoit; pJiero, I carry). This term is applied to the 



Medusce, or Jelly-fishes, from their form ; and it is sometimes used to designate 



