MOLLUSCA.—CLASS IV. PTEROPODA. 209 
HYALAA, Lamarck. 
Testa globosa, inferné rubro-ferruginosa, superné pallidior ; anticé inflata, 
subrostrata, posticé plana, tridentata, dente centrali validissimo, 
apice pervio ; apertura lineari, utrinque extensa. 
The shell of the Hyalea was confounded by the author of the ‘ Systema 
Nature’ with the Terebratule in his genus Anomia, and it appears to have 
been some time before naturalists were at all aware of the nature of its 
animal inhabitant. Bruguiére, evidently incredulous of their affinity with 
the Terebratule, seems to have omitted any mention of the shell in ques- 
tion ; he judged, advisedly no doubt, that it was not of bivalve structure. 
Lamarck introduced the genus Hyalza for the sake of distinguishing this 
seemingly anomalous production, but he skilfully laboured to the last to 
prove it to be a modification of the shell of Terebratula. The investigations 
of Cuvier, De Blainville, Rang and others, have, however, fully deter- 
mined its separate and distinct nature ; and when the univalve structure 
of this shell is considered, coupled with the fact of its never being found 
attached to any marine substance, we almost wonder that its real cha- 
racter should have so long eluded the ingenuity of their predecessors. 
The habits of these singular mollusks have been already noticed in our 
observations on the Pteropoda generally ; it, therefore, only remains for 
us to describe the shell of Hyalzea as being of a globose form, reddish- 
brown on the undermost part, and of a paler colour on the uppermost ; 
the anterior portion of the shell is inflated, and somewhat curved or 
beaked, and the posterior portion is flattish and tridentated, the centre 
tooth being the strongest, and open at the end ; the aperture is linear, 
and extends from side to side. 
Examples. 
Pl. CCXCV. Fig. 1. 
Hyat#a tTRIpENTATA, Lamarck, Anim. sans vert., new edit., vol. vil. 
