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GLOSSARY. 



ORTHOCERATID.E (Gr. orthos, straight ; Jceras, horn). A family of the Nau- 



tilidce, in which the shell is straight, or nearly so. 

 ORTHOPTERA (Gr. orthos, straight ; pteron, wing). An order of Insects. 

 OSSICULA (Lat. diminutive of os, bone). Literally small bones. Often used 



to designate any hard structures of small size, such as the calcareous plates 



in the integument of the Star-fishes. 

 OSTRACODA (Gr. ostrakon, a shell). An order of small Crustaceans which are 



enclosed in bivalve shells. 

 OTOLITHS (Gr. ous, ear ; and lithos, stone). The calcareous bodies connected 



with the sense of hearing, even in its most rudimentary form. 

 OVARIAN VESICLES or CAPSULES. The generative buds of the Sertularida. 



PACHYDERMATA (Gr. pachus, thick ; derma, skin). An old Mammalian order 

 constituted by Cuvier for the reception of the Rhinoceros, Hippopotamus, 

 Elephant, &c. 



PALAEONTOLOGY (Gr. palaios, ancient ; and logos, discourse). The science of 

 fossil remains or of extinct organised beings. 



PALJEOTHERID.E (Gr. palaios, ancient ; ther, beast). A group of Tertiary 

 Ungulates. 



PALAEOZOIC (Gr. palaios, ancient ; and zoe, life). Applied to the oldest of the 

 great geological epochs. 



PALLIOBRANCHIATA (Lat. pallium ; and Gr. bragchia, gill). An old name for 

 the Brachiopoda, founded upon the belief that the system of tubes in the 

 mantle constituted the gills. 



PALLIUM (Lat. pallium, a cloak). The mantle of the Mollusca. Pallial : 

 relating to the mantle. Pallial line or impression : the line left it) the dead 

 shell by the muscular margin of the mantle. Pallial shell ; a shell which is 

 secreted by, or contained within, the mantle, such as the " bone " of the 

 Cuttle-fishes. 



PALPI (Lat. palpo, I touch). Processes supposed to be organs of touch, 

 developed from certain of the oral appendages in Insects, Spiders, and Crus- 

 tacea, and from the sides of the mouth in the Acephalous Molluscs. 



PAPILLA (Lat. for nipple). A minute soft prominence. 



PARAPODIA (Gr. para, beside ; podes, feet). The imarticulated lateral loco- 

 motive processes or " foot-tubercles " of many of the Annelida. 



PARIETAL (Lat. paries, a wall). Connected with the walls of a cavity or of 

 the body. 



PATAGIUM (Lat. the border of a dress). Applied to the expansion of the in- 

 tegument by which Bats, Flying Squirrels, and other animals support them- 

 selves in the air. 



PATELLA. The knee-cap or knee-pan. A sesamoid bone developed in the 

 tendon of insertion of the great extensor muscles of the thigh. 



PECTINATE (Lat. pecten, a comb). Comb-like ; applied to the gills of certain 

 Gasteropods, hence called Pectinibranchiata. 



PECTORAL (Lat. pectus, chest). Connected with, or placed upon, the chest. 



PEDAL (Lat. pes, the foot). Connected with the foot of Mollusca. 



PEDICELLARLE (Lat. pedicellus, a louse). Certain singular appendages found 

 in many Echinoderms, attached to the surface of the body, and resembling 

 a little beak or forceps supported on a stalk. 



PEDICLE (Lat. dim. of pes, the foot). A little stem. 



PEDIPALPI (Lat. pes, ,foot ; and palpo, I feel). An order of Arachnida com- 

 prising the Scorpions, &c. 



PEDUNCLE (Lat. pedunculus, a stem or stalk). In a restricted sense applied 

 to the muscular process by which certain Brachiopods are attached, and 

 to the stem which bears the body (capitulum) in Barnacles. 



PEDUNCULATE. Possessing a peduncle. 



PELAGIC (Gr. pelagos, sea). Inhabiting tbe open ocean. 



PELVIS (Lat. for basin). Applied, from analogy, to the basal portion of the 

 cup (calyx) of Crinoids. The bony arch with which the hind -limbs are 

 connected in Vertebrates. 



PERENNIBRANCHIATA (Lat. perennis, perpetual ; Gr. bragchia, gill). Applied to 



