GLOSSARY. 



843 



out between the septa (see also II., 

 20). 

 Nymphce — in pelecypod shells, the thick- 

 ened ridges on the cardinal margins 

 to which are fastened the edges of 

 the ligament. 



Oak Grove beds — upper Oligocenic of 



Gulf coast. 

 Oakville — upper Miocenic of Gulf 



states. 

 Obconical — inversely conical ; apex 



downward. 

 Oblate — flattened at the poles. 

 Obolelloid — see I., 177, 3. 

 Obovate — inversely ovate, or egg- 

 shaped. 

 Ocala limestone — lower Oligocenic of 



Gulf coast. 

 Occipital — pertaining to the back part 

 of the head ; in trilobites, applied to 

 the posterior part of the cephalon. 

 Occipital furrow or groove — the 

 transverse groove on the cephalon 

 of trilobites which separates the 

 posterior or occipital or neck ring 

 from the rest of the cephalon (see 

 Fig. 1542). 

 Occipital lobes — in some trilobites, a 

 pair of ovoid, disconnected lobes 

 at the base of the glabella in the 

 neck furrow, developed at the ex- 

 pense of the neck ring ; there is one 

 upon each side of the axis usually 

 just within the dorsal furrow (pres- 

 ent in Proetiis). 

 Occipital ring — the posterior division 

 of the glabella of a trilobite ; the 

 neck ring. 

 Occipital spine — in some trilobites, 

 the spine projecting from the axis 

 of the occipital ring ; the neck 

 spine (see Fig. 1547, a). 

 Ocelli — plural of ocellus. 

 Ocellus — a little eye. One of the mi- 

 nute single eyes of many inverte- 

 brates, such as crustaceans and in- 

 sects. Also one of the many simple 

 eyes which form the compound eyes 



of many of the same animals (see 

 Fig. 1636, b). 



Octo — a prefix, signifying eight. 



Ocular — pertaining to the eye. 



Ocular plates — in echinoids, the 

 lower of the two circles of plates in 

 the apical system ; they are situa- 

 ted radially upon the ends of the 

 ambulacra ; called also radial plates 

 (see Fig. 1935, r). 

 Ocular ridge — in trilobites, the ridge 

 passing from the anterior part of 

 the glabella to the anterior end of 

 the palpebral lobe (see Fig. 1584, 

 a). 



Odontophore — in gasitropods, the pul- 

 ley-like ridge of cartilage over which 

 is moved the radula or lingual ribbon. 



Ohio shale — upper Devonic of Ohio, 

 etc. 



Old — a suffix, meaning in the form of. 

 (From. Greek eidos, appearance, pre- 

 ceded by o as the stem vowel (origi- 

 nal or supplied) of the preceding ele- 

 ment of the compound. In contrac- 

 tion, (? -f ei = oi. For example, an- 

 thropo-eidos becomes anthropoides or 

 anthropoid in English.) 



Olean conglomerate — upper Potsville of 

 southern New York. 



Olentangy formation — upper Devonic 

 of Ohio. 



Oneonta sandstone — upper Devonic 

 (Portage). 



Oneota dolomite — lower Ordovicic of 

 upper Mississippi Valley. 



Onondaga limestone — middle Devonic 

 of New York, etc. 



Ontogeny — the life history of an indi- 

 vidual organism ; it is divided into 

 the following five periods: (i) Em- 

 bryonic, from the fertilized egg to 

 and including the formation of the 

 embryonic shell (protoconch, etc.), 

 in mammals the ovarian stage ; (2) 

 Nepionic, baby stage; (3) Neanic, 

 adolescent; (4) Ephebic, adult; (5) 

 Gerontic, old age. 



Operculiform — resembling a lid or oper- 

 culum. 



