CHAP. X. HYREN-E AND INIOXIN-E. i>S5 



species, four of which are from India, and two from 

 Australia. Thev are short, roundly oval shells, with 

 the umbones well defined, and placed towards the 

 middle: from this results their pecuHar character. The 

 lateral teeth are short, and not a great deal longer than 

 the cardinal teeth ; these latter being strong and thick, 

 without being short : they are much crenated, yet 

 %vithout any ridge ; so that they have the appearance of 

 being broken off. Their immediate affinity to Iridea 

 is proved by the Xala elongata, from Xew HoIIaiid, 

 ha^■ing the form of one type, and the teeth of the other. 

 This interesting species, once the property of admiral 

 BUgh, was purchased by us at his sale. The pecu- 

 liarities of Lamarck's Unio Aitstralis {Ilijndella Sw.), 

 and its affinity to Iridea, lead us to arrange it as the 

 anodontine type of the Hyrian^, although it may pos- 

 sibly be an aberiant example of Iridea : the bosses, how- 

 ever, are not striateil, and the whole shell has very much 

 the aspect of an Anodon. Of the fifth type, connecting 

 this sub-family to the next, we know nothing more than 

 what has been already stated. As the remaining genera 

 of the UnionidiT are neither rich in the number of their 

 forms, nor abundant in their species, we shall mention 

 them with more conciseness. 



(-260.) Accortling to the views here taken of the 

 HvRixjE, we may thus compare the four genera, just 

 defined, wi[h the circle of the Uxiomx-e. 



Analogies of the Hyrinj: and the Uniomn-e. 



Genera of the , ;_ . GiHieraofthe 



Ca<tkli\ r Shell trigonal; pcksterior side^ r,-.,. 



V.AJ-TAHX. ^ truncate and short. V -t-cHA. 



Hykiv. Posterior side lengthened. Umo. 

 ? PoroMiDA. 



llYRiPELLA f Compressed, broad; bcvsses not] Lymvvdii. 



inRiPELLA. ^ stnatevl,retuse; teeth slender, j ^^»^^DtA. 



C Lengthenevi oblong ; bosses small; "i 

 •s inner cardinal teeth very small, J- 

 C almost obsolete. j 



