GLOSSARY. 579 



those Amphibia in which the gills are permanently retained throughout 



life. 



PERGAMENTACEOUS (Lat. pergamena, parchment). Of the texture of parchment. 

 PERIOSTBACUM (Gr. peri, around ; and ostrakon, shell). The layer of epidermis 



which covers the shell in most of the Mollusca. 



PERISOME (Gr. peri ; and soma, body). The coriaceous or calcareous integu- 

 ment of the Echinodermata. 

 PERISSODACTYLA (Gr. perissos, uneven ; daklulos, finger). Applied to those 



Hoofed Quadrupeds (Ungulata) in which the feet have an uneven number 



of toes. 



PETALOID. Shaped like the petal of a flower. 

 PHALANGES (Gr. phalanx, a row). The small bones composing the digits of 



the higher Vertebrata. Normally each digit has three phalanges. 

 PHANEROGAMS (Gr. phaneros, visible ; gamos, marriage). Plants which have 



the organs of reproduction conspicuous, and which bear true flowers. 

 PHARTNGOBRANCHII (Gr. pharugx, pharynx ; bragchia, gill). The order of 



Fishes comprising only the Lancelet. 

 PHARYNX. The dilated commencement of the gullet. 

 PHRAGMACONE (Gr. phragma, a partition ; and konos, a cone). The chambered 



portion of the internal shell of a Belemnite. 

 PHYLACTOLJEMATA (Gr. phulasso, I guard ; and laimos, throat). The division 



of Polyzoa in which the mouth is provided with the arched valvular process 



known as the "epistome." 



PHYLLOPODA (Gr. phullon, leaf ; and pous, foot). An order of Crustacea. 

 PHYSOPHORID.S: (Gr. phusa, air-bladder ; and phero, I carry). An order of 



Oceanic Hydrozoa. 



PHYTOID (Gr. phuton, a plant ; and eidos, form). Plant-like. 

 PHYTOPHAGOUS (Gr. phuton, a plant ; and phago, I eat). Plant-eating, or 



herbivorous. 



PINNATE (Lat. pinna, a feather). Feather-shaped : or possessing lateral pro- 

 cesses. 

 PINNIGRADA (Lat. pinna, a feather ; gradior, I walk). The group of Carni- 



vora, comprising the Seals and Walruses, adapted for an aquatic life. Often 



called Pinnipedia. 



PINNULE (Lat. dim. of pinna). The lateral processes of the arms of Crinoids. 

 PISCES (Lat. piscis, a fish). The class of Vertebrates comprising the Fishes. 

 PLACENTA (Lat. a cake). The " after- birth," or the organ by which a vascu- 

 lar connection is established in the higher Mammalia between the mother 



and the foetus. 



PLACENTAL. Possessing a placenta ; or connected with the placenta. 

 PLACOID (Gr. plax, a plate; eidos, form). Applied to the irregular bony 



plates, grains, or spines which are found in the skin of various fishes 



( Elasmobranchii) . 

 PLAGIOSTOMI (Gr. plagios, transverse ; stoma, mouth). The Sharks and Rays, 



in which the mouth is transverse, and is placed on the under surface of the 



head. 

 PLANTIGRADE (Lat. planta, the sole ef the foot ; gradior, I walk). Applying 



the sole of the foot to the ground in walking. 



PLASTRON. The lower or ventral portion of the bony case of the Chelonians. 

 PLATYRHINA (Gr. platus, broad ; rhines, nostrils). A group of the Quadrumana. 

 PLEURODONT (Gr. pleuron, rib, side ; odous, tooth). Having the teeth anchy- 



losed with the inner side of the jaws. 



PLEURON (Gr. pleuron, a rib). The lateral extensions of the shell of Crustacea. 

 PNEUMATIC (Gr. pneuma, air). Filled with air. 

 PODOPHTHALMATA (Gr. pous, f oot ; and ophthalmos, eye). The division of 



Crustacea in which the eyes are borne at the end of long footstalks. 

 POLLEX (Lat. the thumb). The innermost of the five normal digits of the 



anterior limb of the higher Vertebrates. In man, the thumb. 

 POLYCYSTINA (Gr. polus, many ; and kustis, a cyst). An order of Protozoa, 



with foraminated siliceous shells. 

 POLYPARY. The hard chitiuous covering secreted by many of the Hydrozoa. 



