836 



NORTH AMERICAN INDEX FOSSILS. 



Hyponome — water tube of squids, cut- 

 tle fish and other cephalopods ; am- 

 bulatory funnel (see Fig. 1230). 



Hyponomic sinus — see sinus. 



Hypostoma — the upper lip of trilobites ; 

 it is attached to the under folded an- 

 terior margin (doublure) of the 

 cephalon, and is usually found de- 

 tached. It corresponds to the labrum 

 of other arthropods. Also spelled 

 hypostome (see Figs. 1556, e, IS59). 



Hypozygal — for use in crinoids, see II., 

 490. 



Im — a form of the prefix in. 



Imago — the adult stage of an insect. 



Imbricate — to overlap in series. 



Imperforate — without an opening. In 

 echinoids, referring to the interam- 

 bulacral areas and also to the ab- 

 sence of a pit in end of a mamelon. 



Implantation — planting between, as 

 when a new plication suddenly ap- 

 pears between two older ones. 



Impressed zone — in cephalopods, see 

 II., 18, bottom. 



In — a prefix, meaning not or in. 



Inarticulate — not united by teeth and 

 socket. 



Incised — cut into. 



Incrusting — covering as with a crust. 



Index fossil — see fossil. 



Inequilateral — having unequal sides ; 

 see equilateral. 



Inferior — lower in position. 



Inferradials — for use in crinoids, see 

 IL, 489. 



Inflated — swollen. 



Inflected — bent or turned inward or 

 downward. 



Infra — a prefix, meaning below, after. 



Infrabasals — in crinoids, with dicyclic 

 base, the lowest cycle of plates (see 

 Figs. 1804, 1876). 



Inhalent — in sponges, applied to canals 

 or pores with inflowing current (see 

 Fig. 21). 



Ink-bag — the organ present in most di- 

 branchiate cephalopods, as the squid. 



which secretes a brownish black 

 fluid (sepia). 



Inosculate — to connect so as to have in- 

 tercommunication. 



Inter — a prefix, meaning between. 



Inter ambulacra — in echinoids, the five 

 broad areas separating the ambulacra 

 (see Fig. 1920). In crinoids, see II., 

 491. 



Interambulacral — referring to the in- 

 terambulacra. 



Interbrachials — plates in the calyx of a 

 crinoid lying between the brachials. 



Intercalation — the insertion of any- 

 thing among others. In the normal 

 enlargement of a shell, the radiating 

 ribs or plications may increase in 

 number by the dividing of the older 

 ones or by the intercalation or im- 

 plantation of new ones. 



Intercellular — between the cells. 



Intercostals — in crinoids, the plates ly- 

 ing between the costals (see II., 491). 



Interdistichals — plates in the calyx of a 

 crinoid lying between the distichals. 



Interlamina — plates between scales or 

 plates. 



Internode — for use in crinoids, see II. , 

 488. 



Interporiferous area — in echinoids, that 

 portion of the ambulacrum lying be- 

 tween the poriferous zones or areas, 

 from which protrude the tube feet 

 (see Fig. 1920, d). 



Interradials — plates in the calyx of a 

 crinoid lying between the radials. 



Interstitial — pertaining to an interven- 

 ing space between lines, plications, 

 etc. 



Interzoecial — between the zoecial tubes 

 in Bryozoa, etc. 



Intra — a prefix, meaning within. 



Intrathecal — within the theca ; endo- 

 thecal. 



Introverted — turned inward ; in brach- 

 iopods, referring to the spiral brach- 

 idia when turned apex to apex (see 

 Fig. 38s, e). 



Invaginated — inserted as in a sheath. 



Involute — rolled inward; applied to 



