II AITKK \ I. 



^ __^__ ^^___^^A 



Till-: LOWER SILURIAN i.AMKi.u r.u.\\M IIATA 



>l- MI\M-> >TA 





\ number <>f name- fur this class of molln-k-. commonly known us niu- 

 have. fniiii time to time. been proposed. Init none of them, save Hlainville's L<ninlli- 

 l>rnn' hintti. which, on the whole, is an appropriate designation, has enjoyed more 

 than merely temporary popularity. Of the other names, that, proposed by (ioldfn 

 in 1" done presents fair claims to recognition. -ince it> adoption would 



produce that most desirable element uniformity, in the terminology of the varion- 



Ml compri-ed in the suhkinplom Mnllnsra. Hlainville's name, however, has six 

 year and is so well established in literature that it is doubtful if the con- 

 fusion which would result fr a change of names would be -utliciently compensated 



for by the superior advantages of Goldfuss* term. 



The Limellibranchiata agree with the Brachioixxla in having Itivalved shell-. 

 Init .litter in having them, as a rule, e|iial and inequilateral instead of ine<|iii\alved 

 and equilateral: they are, furthermore, placed on the sides of the animal (for which 

 reason we distinguish them as right and />v/). instead of above (dorsal) and below 



tral). From t he Gastropoda and Cephalopoda they are distinguished by wanting 

 a distinct head, in having bivahed -hells, a bilohed mantle and lamelliform gills 

 developed in pair-. 



icnilly the animal illy developed, of oval, rounded or ti 



versely elongate form, laterally compressed and enclosed in the two fleshy, often 

 more or less united. lol>es of the mantle. Within the latter, which are attached to 

 and secrete the calcareou- or perlaceous valves, we have first the lamelliform gills. 

 and between these the wmou- internal : a> the heart, intestines and 



organs Of generation, and the month and anal opening, and usually also a protru-ible 

 muscular foot Numerous moditicat ions of the mantle lobe- , - uesthey 



are separate, at other times their mai . Aether so as to enclose the 



animal as in a sack. In th> COM an opening is toft in front for the 



