30 



are sub-sessile, while in most of the Anatinidse they are long; and only the branchial siphon 

 is surrounded by tentacles, but not the anal ; while the openings for both siphons in the Ana- 

 tinidffi are fringed, or furnished with tentacles. These differences appear however to be of 

 secondary importance; and on that account the animal may be referred to this family. On 

 the contrary, it cannot be placed among the Trigonidse, Cyprinidse or Cardiidse, to which the 

 several authors have referred this genus; as the animals of the said three families have the 

 lobes of their mantles separate, and equal shells. 



Of our native genera the genus Pecchiolia seems to stand nearest to the genus 

 Lyonsia, Turt., from which it differs in the following points : the shell is much shorter, not 

 gaping, the right shell is larger than the left (the contrary is the case in the Lyonsia) the 

 umbones lie quite in front near the anterior extremity of the shell, and are somewhat spirally 

 involved. The animal has separate siphons (in the Lyonsia they are united nearly in their 

 whole length) of which the anal is prominent, and the branchial sessile having its opening 

 surrounded by pinnate tentacles covered with papillae (the tentacles of the Lyonsia are simple 

 smooth threads) and the anal is without tentacles (which exist in the Lyonsia). The foot is 

 slender cylindro-conical with blunt rounded end, (in the Lyonsia it is tongue-shaped and flat) 

 and the aperture in the mantle through which it is extended, has an entire border (in the 

 Lyonsia it is according to Forbes &Hanley fringed); the lip tentacles appear to be rudimen- 

 tary or wanting (in the Lyonsia they are said to exist and to be triangular, slender and 

 folded on the interior side). The circle of simple tentacles, on the border of the mantle, 

 surrounding the siphons, seems also to be wanting in the Lyonsia. 



It may further be remarked in conclusion that the conchifer now under examination 

 has with respect to its shell considerable resemblance with the genus Mytilimeria Conrad, 

 which (for the animal seems to be unknown) is referred by Woodward to the Mytilidse, but 

 byChenu (I. c. p. 39) certainly more correctly to the Anatinidse, with the following characters: 

 ,,The shell roundish (subarrondie) more or less inflated, equivalve, fragile, covered with a thin 

 ,,caduke epidermis. The umbones subspiral; the hinge without teeth, but formed only of 

 ,,small linear excavations under the umbones to receive the ligament, which contains a small 

 ,,bone (osselet). The muscular impressions small ; the mantle-impression with an obtuse sinus." 

 M. Nuttalii Conrad, fig. 175. 



