olU'KK I 



IMMONODESMACKA 



385 



out epidermis ; >> amphidetic or obxcm, : //,/,/, ,,t /,<,,->',>', -nl,,,-, i>-/.i//v opiathodetic 

 and external ; </>'//> usually filibranchiatt ; innnfle lobes without ocelli, more or less free, 



,/,,n i-nllif ir/'tlt tin i' mil xijihon complete mnl th< l,ru,irhi<il ///(-,////,/</. .- fi,,,t 



fiii-iii, i/ronri'tl, ////xs//"' /v,//.s- ; ,nn,in> riunx ; mostly TIKI li m. 



Family 38. Modiolopsidae. Fi.-clicr emend. 



Shell Modioliform, usually e.(/nimli-i, //<, thin, with sub-cij""! mlilnrti,/- scars; 

 ligament deep-seated ; hinge edentulous or Difmnloiif : sometimes byssiferous. Silurian to 

 Cretaceous. 



The heavier forms show an obtuse ridge or two extending fnuu tin- l"-ak- t<>\\urd the basal 

 margin. The pedal scars are separate from and behind the anterior adduet.r>. The 

 included here appear to be 

 the prototypes of the .!///- 

 fi/ii/<f, from which they 

 differ chiefly in those char- 

 acters that are common to 

 most of the ancient types, 

 such as the sub-equality of 

 the adductor scars and their 

 more dorsal situation. The 

 recent Idas is very similar. 



Modiolopsis, Hall (Fig. 

 677). Valves elongate- 

 oval, closed, with nearly 

 terminal beaks, narrow 

 hinge plate, and edentul- 

 ous hinge. ? Ordovician ; 

 Silurian. 



Modiomorpha,, Hall. 

 Similar, but with a wider 

 hinge plate, and single, 

 oblique, elongate, posterior 

 ridge - like tooth. De- 

 vonian. sp. OrdnVH.ian 



clnnatl, Ohio. */! 



FIG. 



Cin- 



Fir;. 



Mi/<M"iin-l,ii .-ti-lntntii, Goldf. 

 Oolite; Bayeux, Calvados, l/j. 





Afyoconeka, Sow. (Fig. 

 678). Hinge usually with an elongate cardinal, and a long, weak, lateral t<ith in tin- 

 right valve ; otherwise resembling Modiolopsis. Carboniferous 

 to Cretaceous. 



? Hi/>/i/i<x/i'iiiii, Sow. Thiek, inflated, ovate, concent rie- 

 ally waved. Hinge with a long, Muni, oMiijue, caitlinal 

 tooth, or edentulous ; adductor scare strong. Jura. 



Modinluiinii, H'hiteavesia, Eurymya, Arisd'Hn, and Prolo- 

 bella, Ulrich; Goniophora, Phillips. Silurian and Devonian 



Family 3!). Mytilidae. Fleming. 



Shell equivalve, very inequilateral, hetero)ii;i<tri<n>, ,-lnjhtlij 

 <in /> in ;i, tif/iicnlly Dysodont : area amphidetic or none ; ligament 

 itxnufli/ external, deep-seated; rarely with an aliriin-nlnr 

 internal resilium ; pallial line simple; mantle lobes u/utnl 



below the aim/ *ii>lnt, otherwise free; qenerally byssiferous. 

 itytUut*uMaevt8,Bow. Great -p, ,, 



Oolite; Minchinluimpton, Eng- Devonian to Kecent. 



Mytilus, Linn. (Fig. 679). Shell elongated, thin, with 



terminal pointed beaks ; valves wider and rounded behind, gaping a little for the 

 VOL. I 2 C 



