ad I 





|..-.lal niiiM-le KW, IWenor adductors large. MTV famf!\ impressed, s lew 



than their diameter from the posterior extremity of tin- h.iu 



lm "' r * f rmlw> *"Hv with on,, or two obtuse ridge-like tin- 1,,,^ 



from tin- U'.ik> ..l.li,,n,.ly l.ackward toward tln< . f the ventral n 



Of the WHOM genen included . this family in the srh, , ,, 



pa Hi' K\ I am -ati-lied t hat some of those preceded I._V aquation maik will lie MI. 



or later placed cU.'where. No more -at i -factory arrangement having suggested it 

 the\ W,MV i-efenv.1 here, because thoir known characters agree with one or anotl.rr 

 f the more typical genera. Tim-. AH**tU*, a>idr from it- unequal vai 



l- l' an ^ faviiraMy with Kurym ndella seems to be related to Mml,- 



/ " / - al " ' V'xliolopgu and Cymatonota, while Psiloconcha, in a gen 



way. resemliles Aifimnmfn. Hut of I'l/iinontyn too little is known to venture an 

 o|iinion as to its ultimsite placement, the only excuse for recognizing the genus in 

 thi- ronneetion being that it would be even more out of place in any of the other 

 familie-. The po-ition of I'rolobella also is quite uncertain. 



ie of the species of Modiolopsis remind us so strongly of Modioln ami Mij,H-vnd,,i 

 that we can scarcely escape the conviction that the latter genera, which are placed 

 in the families Myiili,l,i ami I'msinMr by Stoliczka and Xittel, have 

 really descended from Modiolopsis. Still, I am of the opinion that the paleozoic 

 M constitute a more natural grouping by themselves than can be attained !> 

 any of the courses adopted heretofore. The position usually assigned to .l/</;W/wia 

 i- near Modiohi in the family Mi/filiJir, l.ut Stoliczka and Zittel see greater reseui- 

 I'lanees with Myoconcha ami therefore regard the genus as an early type of the 

 I'xtsinidi?. But both of these families, the first in partiulur, seem to me to include 

 heterogeneous material, and if they were revised according to the genesis of 

 I.imelliliram-hiata. I have no doubt their limits would be greatly modified. 



The first reason to influence me for the separation of Modioloptu from tin- 

 MytUida occurred during; a comparison with Mynlimi. K on i nek, a genus that, whih- 

 it seems to be very ju>tly as- ith Mi/tilii*. has no relation to Modtoloptit. 



lnil>ed, according to my xicu. the progenitors of M : i,ilinn are to be Bought for 

 aiming the . lwi//N/c////W'/. 



Next, a comparison with recent -pecit - of Mixlinln proved that while a general 

 inlilance obtaineil there were >tii :i features in which the genera here 



-ed as the Moiliulujixidof agreed thoroughly among themselves and differed from 

 f'l. Thus, in the latter, ami : true of all the MytUi>l>r. the ante' 



aililm-tor impre>-inn i- ai\\a\- -mailer ami the posti 



t lie canlinal margin as well a> of a >hapr. ini-luding the prolongation fonne<i 

 P-ilal mn-cles, never seen in the paleo/on- -lidK umlcr con-i<> "n tlu'wi 



