MODIOLA. 193 



Mr. Alder, who made an accurate drawing- of the type, 

 whilst temporarily in his possession, has transmitted us a 

 foreign shell, which, on comparison, he at that time re- 

 garded as identical with it. This is the M. agglutinans 

 of Cantraine, (Bulletin Acad. Sciences Naturelles de Bru- 

 xelles, 1835, ii. p. 398) subsequently (1844) and provision- 

 ally termed vestita, in the second volume of his admirable 

 work upon Sicilian shells (En, Moll. Sicil. vol. ii. p. 51, 

 pi. 15, f. 12), by Dr. Philippi, who had lost the name under 

 which he had received it from Malta. As that species 

 was also unhesitatingly pointed out by Mr. Thompson, well 

 acquainted with Mr. BalPs example, in Mr. Cuming's 

 ample collection of exotic Modiolce, we have appended a 

 careful description of it, since the excellent Latin one of 

 the German naturalist may not be in the hands of many 

 students of British Oonchology, with the aim of enabling 

 any fortunate discoverer of further examples of Ballii, 

 to determine with still greater exactitude its relation with 

 the curiously encased Mediterranean shell, which imbeds 

 itself in a felt-like ball or coccoon, entangling or immeshing 

 stones fragments of other shells and various marine bodies 

 in its external coating. 



Oblong, slightly cylindraceous, rather oblique, thin, ven- 

 tricose, covered with a shining yellowish chestnut ejjider- 

 mis, under which the surface has an uniform whitish hue ; 

 concentrically marked with rather distant wrinkles of in- 

 crease, which are usually obsolete in the younger examples, 

 but entirely devoid of folds, undulations, or any other kind 

 of sculpture. Surface diagonally divided into two areas, 

 (of which the posterior is manifestly the larger, and the 

 more convex) by the abrupt frontal elevation of the broad 

 umbonal fold, the upper portion of which presents likewise, 

 in the adult, a brighter and more yellow cast of colouring. 

 Hinder dorsal edge nearly straight, and a little elevated, 

 rather long in the young, about equal to the arcuated pos- 

 terior margin in the adult. Ventral edge slightly lobed 

 behind, obliquely ascending in front. Anterior side, though 

 very short, distinctly projecting, unsymmetrically rounded 



