'II \ UBBOIOP i .. 



Monograph of the /''///////>. /H.^niiilu-. Jefl'rei/xii.he, Skeneidoe, 



inn! 



I \MILY RIS80IIDJE. 



Aninuil with a more or less elongated mu//le; elongated, cylin- 

 drical tentacles, with the eyas on swellings at their outer bases; 

 male origin i cxserted, situated at a considerable distance be- 

 hind the right tentacle; gills both pallia!, the right one largest, 

 rather .-hurt and broad, composed of few lamina-, which are much 

 broader than high ; foot oblong, punctate before, rounded or 

 pointed behind; operculigcrous lobe well developed < )pcrculuin 

 corneo!i>, paucispiral. Dentition ( 1*1. 54, fig. 98.) 



Shell small, usually turbinate or elongate, often more or less uni- 

 bilicated; peristome continuous, more or less rounded, never truly 

 channeled in front. 



The I\issoiid:e are small, often minute, phytophagous marine mol- 

 Insks. inhabiting all parts of the world, frequenting alg:c, /ostera, 

 etc., from which they often suspend themselves by a mucous fila- 

 ment. 



Formerly a large number of fresh and brackish-water forms were 

 here included, which, although nearly allied both as to animal and 

 shell, are now perhaps more properly considered to form a family 

 apart llydrobiidie: these will be considered in the series of the 

 .Manual devoted to Fresh Water Mollusks. 



The Kioiid;e have been monographed by: Schwart/ von Mohren- 

 . Denkschriften K. Akad. Wissen, 1K(>0-II4. 



8 \\erby, in Reeve's Cotichologia Inmica. \\. IL'.'!. sp. No date. 



Wcinkaiilf, in KiiMer's Conch. Cab., "21 '\ species, 1 S 7'i. 



/x of Genera and Subordinate Gronj>.. 

 Genus 1MSSOIA. Kremenville. 1S14. 



Shell imperforate or subperfbrale, more or less obhuig. tnrbinated, 

 usually thick, white or conn-mis, smooth, ribbed or cancellated, 

 aperture entire, oval, peristome thick, simple or reflected. Oper- 

 culnrn corneous paucispiral (PI. .VI. fiu r . 9 



The animal has long, slender tentacles, sometimes ciliated, with 



on sm;il] prominences near their outer bases; mantle with a 



tentacular appendage in front, on the right side, or on either side ; 



toot truncate in front, attenuated behind, with a glandular sulcus. 



