ERYCINID^. 219 



sitic. In one sense only can it be said to live on echinoderms. 

 The food of Spatangas piayureus, on which it is usually found, 

 appears to consist of animalculoe ; and for that purpose it 

 swallows large quantities of shell-sand, causing thereby a strong 

 and frequent current in the neighborhood of its mouth. The 

 Montacuta probably aA^ails itself of this in-draught, and partakes 

 of the sustenance intended for the Spatangus, placing itself in 

 the way, with its alimentary tube or opening turned in the right 

 direction. No exudation of the Spatangus has been noticed ; 

 and its excretions would scarcely be produced in sufficient 

 quantity for the support of the Montacuta, or perhaps be suitable 

 to it. The latter has no suctorial organ, such as is possessed by 

 all animal parasites ; it never attaches itself to the pedicellarige 

 or any other soft part of the echinoderm ; nor has it once been 

 detected on the back or sides, or elsewhere than in the ventral 

 region of its associate. It is only found on the spines close to 

 their points." — Jeffreys. 



TELLTMYA, Brown, 1827. Shell transversely oval, surface a little 

 rugose ; beaks prominent, acute ; hinge with a pit for the liga- 

 ment, which contains a small ossicle, and a triangular cardinal 

 tooth on each side of it in the right valve, and two distant rudi- 

 mentary lateral teeth in the left valve. T. bidentata, Mont, (cxx, 

 86). Europe. 6 sp. Eur., Cal., Japan. 



Kelliella, M. Sars. 



Distr. — K. miliaris, Phil, (cxx, 8t-89). Europe. 



Shell minute, orbicular, tumid ; umbones slightly prominent, 

 incurved ; lunule cordate, distinct ; ligament minute ; surface 

 white, without epidermis, eoncentricall}^ striate ; cardinal teetli 

 two, laterals none. 



Las^a, Brown, 1827. 



Syn. — Poronia, Recluz, 1843. Cycladina, Cantr. (pars). Kellia 

 (pars). Bornia (pars). 



Distr. — 9 sp. Universal. Fossil ; Tertiary. L. rubra, Mont, 

 (cxx, 90). 



Animal with the mantle folded on the anterior side so as to 

 form a wide but incomplete incurrent tube ; the excurrent tube 

 is inconspicuous, placed on the opposite side ; foot long. 



Shell minute and roundish oval ; beaks straight ; cartilage long, 

 placed at the shorter end of the shell, contrary to that in Kellia ; 

 left valve with a minute thorn-like cardinal tooth ; and in each 

 A^alve two remarkably strong lateral teeth. 



The genus is intermediate between Montacuta and Kellia. 



"The Lasseae usually inhabit the littoral zone, where they con- 

 gregate in vast numbers at the roots of small sea-weeds, in the 

 crevices of rocks, and in empty shells. L. rubra, a British spe- 



