COMPENDIUM OF GENERIC DISTINCTIONS. 



785 



Suo-orek*. TECTI-RRANCffIATA.G\\\s covered by 

 shell or mantle. 



Family. BULLION. Shell rounded, thin ; spire small ; 

 aperture long, rounded, and waved in front. Animal investing 

 shell : disc-like head ; eyes none, or in disc. One gill on right 

 of back. Edge of mantle overlapping shell. 



Genus. BULLA. Shell oval, swollen, partly invested by 

 animal ; aperture larger than shell. Head-disc two-lobed 

 behind. Warm and hot seas. 



Genus. CYLICHNA. Shell cylindrical ; aperture narrow and 

 rounded in front. Animal not investing shell. Many parts of 

 world. 



Genus. APLUSTRUM. Shell oval, swollen ; aperture blunt 

 in front : outer lip sharp. Foot capable of investing the whole 

 shell. Warm seas. 



Genus. PHILINE. Shell oblong ; aperture very wide in 

 front. Head large and oblong ; eyes none ; foot short and 

 broad. Warm and temperate seas. 



Family. APLYSIAD^E. Shell none, or small and covered 

 by mantle. Animal like slug ; head distinct ; foot long, form- 

 ing tail behind. Very large lobes at sides. 



Genus. ApLYStA. Shell oblong, flexible, translucent. 

 Animal oval ; neck long ; four tentacles. Sides with large 

 lobes used as fins ; gill in centre of back. Most seas. 



Genus. DOLABELLA. Shell hatchet-shaped. Gill near end 

 of body. Hot seas. 



Genus. LOBIGER. Shell oval, transparent ; on middle of 

 back covered with epidermis. Animal slender ; eyes small, 

 on sides of head. Two pairs of rounded lobes on sides. 

 Warm seas. 



Family. PLEUROBRANCHID^E. Shell mostly limpet- 

 like ; mantle covering back ; gill on sides. 



Genus. UMBRELLA. Shell limpet-like, flat, round, and 

 concentric. Foot large, deeply notched in front. Mantle 

 small. Gill on right side, forming a series of plumes. Warm 

 and hot seas. 



Sub-order. NUDIBRANCHIATA.Ko shell in adult. 

 Gills always external on back or sides of body. 



Family 

 back. 



Genus. DORIS. Oval, flattened ; mantle large. Tentacles 

 retractile. All seas. 



Family. TRITON I AD^E. Gills along sides of back ; 

 tentacles retractile. 



Genus. DBNDRONOTUS. Long ; tentacles laminated ; 

 branched appendages in front of head. Single series of gills 

 on each side of back. Northern seas. 



Genus. DOTO. Slender ; sheaths of tentacles trumpet- 

 shaped ; tentacles slender, not laminated. Northern seas. 



Family. BOLID^E. Gills papillose, along sides of back ; 

 tentacles not retractile. No distinct mantle. 



Genus. EOLIS. Rather oval. Gills numerous and over- 

 lapping ; mouth with homy upper jaw. World-wide. 



Genus. GLAUCUS. Long and slender. Gills on three pairs 

 of lateral lobes. Atlantic and Pacific. 



Order. NUCLEOBRANCHIATA. Respiratory and 

 digestive organs forming a kind of nucleus or posterior part of 

 back. 



Family. FIROLID^E. Long, cylindrical, translucent ; 

 ventral and tail fins. Mantle with circular lip. 



Genus. FIROLA. Head long and slender ; fin with small 

 sucker. Tail keeled ; branchial processes numerous, conical, 

 and slender. Tentacles four ; eyes black and distinct. Warm 

 and hot seas. 



Genus. CARINARIA. Shell glassy, limpet-shaped, keeled. 

 Animal large, translucent ; head thick and cylindrical. Warm 

 and hot seas. 



Order. PTEROPODA. Sides towards the front furnished 

 with swimming flaps. 



Sub-order. TffECASOMATA.A.mm*\ with external 

 shell ; head indistinct ; foot and tentacles scarcely visible. 



Family. HYALEID^E. Shell straight, curved globular, 

 or needle-shaped. Animal with two large fins. Body inclosed 

 in mantle. 



Genus. HYALEA. Shell globular, translucent. Animal 

 with long appendages to mantle, passing through slits in shell. 

 Warm and hot seas. 



ily. DORID^E. Oblong ; gills in circle on middle of 

 Tentacles two. Skin with spiculas. 



Genus. CLEODORA. Shell pyramidal, triangular, tip sharp. 

 Eyes and tentacles scarcely visible. Warm and hot seas. 



Genus. THECA. Shell straight, conical, pointed ; aperture 

 triangular. Temperate and warm seas. 



Genus. CYMBULIA. Shell soft, slipper-shaped, sharp in 

 front, blunt behind. Fins large and rounded. Warm and hot 

 seas. 



Order. BRACHIOPODA. Bivalve molluscs, valves un- 

 equal ; mostly toothed. 



Family. TEREBRATULID^. Shell covered with min- 

 ute points ; lower valve with large beak and two hinge-teeth. 

 Animal attached either by footstalk or by ventral valve. Dor- 

 sal valve with hinge and loop. 



Genus. TBREBRATULA. Shell smooth, convex; beak per- 

 forated and blunt ; loop short and attached to hinge-plate. 

 Animal attached by footstalk. Mediterranean. 



Family. RHYNCHONELLID^E. Shell without the 

 points, beaked ; opening behind beak. Hinge-plate deeply 

 divided. 



Genus. RHYNCHONELLA. Shell three-sided, beak sharp; 

 dorsal valve depressed at sides ; ventral valve hollowed on 

 centre. Animal with long spiral arms directed inwards. Most 

 temperate and cold seas. 



Family. LINGULID^E. Shell oblong; attached by foot- 

 stalks passing between valves. Animal with fringed mantle. 



Genus. LlNGULA. Shell compressed, gaping at both ends; 

 dorsal valve rather short. Branchial veins arranged in series 

 of loops. Warm and hot seas. 



Order. CONCHIFERA. Bivalves with body compressed, 

 covered on both sides by a flap of the mantle. Gills at sides of 

 body, under the mantle flaps. Valves connected by an elastic 

 ligament at hinge. 



Sub-order. A SIPHONIDjE. No respiratory siphons. 



Family. OSTREID^E. Valves unequal ; ligament inter- 

 nal ; abductor impression single. Animal marine ; mantle 

 open ; two crescent-shaped gills on each side. 



Genus. OSTREA. Shell attached by left valve ; hinge tooth- 

 less ; structure laminated. Margin of mantle double ; lips 

 plain ; gills nearly equal. World- wide. 



Genus. ANOMIA. Shell thin, translucent, attached by a 

 plug passing through a hole in notch in right valve. Short 

 double fringe on mantle. World-wide. 



Genus. PLACUNA. Shell free, very flat, translucent, 

 rounded, resting on right valve. Indian seas. 



Genus. PECTEN. Shell regular, rounded, mostly ribbed. 

 Animal with a row of black ocelli and a fringe of delicate fila- 

 ments. Gills crescentic and delicate. World-wide. 



Genus. HINNITBS. Shell regular, and with byssus when 

 young, cementing itself and becoming irregular when old. 

 Europe. 



Genus. . LIMA. Shell oblique, oval, front side straight and 

 gaping. Edges of mantle separate, inner fringed with tentacles ; 

 ocelli very small. Europe. 



Genus. SPONDYLUS. Shell irregular, ribbed radiately, 

 rather covered with spines or leaf-like projections. Lips of 

 animal foliaceous. World-wide. 



Family. AVICU LID^E. Valves unequal, oblique, attached 

 by byssus ; hinge-line straight and long, hinge smooth or very 

 slightly toothed^ Foot spinning a byssus. All in tropical and 

 warm seas. 



Genus. AVICULA. Shell obliquely oval ; cartilage pit single, 

 oblique; one or two small teeth on hinge. Adductor impres- 

 sion large, near centre ; pedal small and near umbo. 



Genus. MALLEUS. Shell, when adult, T-shaped. China, 

 Australia. 



Genus. PINNA. Valves equal, wedge-shaped, posterior on 

 side gaping; hinge toothless. Edge of mantle with double 

 fringe ; byssus very large and powerful ; gills long. Many 

 seas. 



Family. MYTILID^E. Valves equal, oval, or long, close 

 throughout ; epidermis thick and dark. Animal spins a 

 byssus ; two gills ou each side ; foot cylindrical and grooved. 



Genus. MYTILUS. Shell pearl-lined, rounded behind, 

 wedge-shaped ; hinge with very small and shallow teeth. Edges 

 of mantle slightly projecting, edges of gills fringed, byssus thick. 

 World-wide. 



Genus. MODIOLA. Shell oblong, widened in front ; hinge 

 toothless ; epidermis often deeply fringed. Most seas. 



