784 



COMPENDIUM OF GENEKIC DISTINCTIONS. 



Family. PEGASID&. Breast very wide ; pectorals long, 

 with nine or ten spiny rays. Mouth below snout (like that 

 ot the sturgeon). Breast-ring very broad, with two spines. 

 Tail-fin v?ith ten strong rays. 



Genus. PEGASUS. As family. Warm seas. 



Family. SYNGNATHIDjE. Body long. No first dorsal 

 or ventral. Anal very small or wanting. Males with egg- 

 pouch. Gill-aperture small and circular. 



Genus. HIPPOCAMPUS. Tail prehensile at tip, without 

 fiu. Hind part of head elevated. Most seas. 



Genus. SYNGNATHUS. Snout long, cylindrical, without 

 opines. Body seven-sided. Most seas. 



Order. GANOLEPIDOTI. Body covered with strong, 

 bony, enamelled scales. 



Genus. LEPIDOSTEUS. Jaws long and narrow. Scales in 

 oblique rows, tending backward. Dorsal small and near tail. 

 Vertebrae extending to upper lobe of tail. North America. 



Order. CYCLOSTOMI Body cylindrical. Branchiae 

 with six or seven spiracles on each side. 



Family. PETROMYZONID.S5. Lip circular or horwo 

 shoe shape. Two dorsals. 



Genus. LAMPETRA (including Petromyzon). Mouth cir- 

 cular, with hard tooth-like processes. Branchial apertures 

 seven. No pectorals or ventrals. Seas and rivers. 



Genus. GEOTRIA. Skin of throat dilated into pouch. 

 Rivers, Australia. 



Genus. AMMOC.ETES. Lip of horseshoe shape. Mouth 

 not toothed. Rivers. 



Genus. MYXINE. Dorsal very long and broad, running 

 round tail. Lip surrounded with barbules. Mouth with a 

 single hook-like tooth, tongue with two rows of teeth on 

 each side. Branchial apertures two. Many seas. 



Order. LEPTOCARDII Pulsating vessel instead of 

 heart ; blood pale. Dorsal cord instead of vertebrae. 



Genus. AMPHIOXDS. Body sharp at both ends. Dorsal 

 running round body. Mouth below, a mere longitudinal 

 slit. Many seas. 



DIVISION INVERTEBRATA. 



Animals without vertebra, true heart, or brain. 



CLASS. MOLLUSCS. 



Invertebrate animals with soft bodies, enclosed in a muscular skin Mostly with an univalve or oivaloe shell. 



Sub-class. CEPHALOPODA. Two sides 

 symmetrical. Jaws powerful and vertical. Eyes large, on 

 sides of head ; cephalic ganglion (i.e. the knot of nervous 

 matter which takes the place of the brain) protected by 

 cartilage. Arms set round head. 



Order. DIBRANCHIATA. Eyes sessile and promi- 

 nent ; jaws horny ; arms with suckers. Two gills. Ink- 

 gland present. 



Section. OCTOPODA.Ai-ma eight; eyes fixed. 



Family. AEGONAUTID^S. Dorsal arms of female 

 webbed at tips, and secreting a delicate shell. Mantle sup- 

 ported in front by a single ridge on the funnel. 



Genus. ARGONAUTA. As family. Warm seas. 



Family. OCTOPODID-ffi!. Arms not webbed, united at 

 rase by mantle. Two short styles in mantle instead of 

 shell. 



Genus. CIRRHOTEUTHIS. Two fins on body. Arms united 

 nearly to tip ; suckers in single row. Northern seas. 



Section. DECAPODA.-A.rm* ten. Tentacles two. 

 Suckers on footstalks. Shell loose in mantle. 



Family. TETJTHID^!. Body long ; fins short and broad. 

 Shell homy. 



Genus. SEPIOLA. Body short; fins on back and 

 rounded. Suckers in two rows or crowded on arms, four 

 rows on tentacles. Many seas. 



Family. SEPIAD5!. Shell chalky. Tentacles long and 

 wide at tips. 



Genus. SEPIA. Body oblong ; fins on side, long as body. 

 Four rows of suckers on arms. Many seas. 



Order. TETRABRANCHIATA. Animal creeping, 

 shell external and chambered. Eyes on footstalks, jaws 

 chalky, arms numerous. Branchiae four. 



Family. NAUTILID-SI. Body-chamber large. Siphuncle 

 internal. 



Genus. NAUTILUS. Few whorls of shell. Warm and 

 tropical seas. 



Order. GASTEROPODA. Sides not symmetrical 

 Broad muscular foot under body. 



Sub-order. PROSOBRANCHIATA. Abdomen large 

 and protected by a large shell. Branchi before the pul- 

 sating vessel. 



Section. SI PHONOSTOMATA. Shell spiral, 

 aperture notched or produced. Opercnlum horny. Gill* 

 placed obliquely over back. 



Family. 6TROMBID.33. Shell with wide and deeply- 

 notched lip. Operculum claw shaped and notched. Eyes 

 large, on footstalks ; foot small and feeble. 



Genus. STROMBUS. Spire short, aperture long, outer 

 lip expanded. Warm seas. 



Genus. ROSTELLARIA. Spire long and many-whorled. 

 Posterior canal running up spire. Warm seas. 



Genus. PTEROCERAS. Outer lip formed into several long 

 claws. India and China. 



Family. MTJRICID/E. Canal straight in front, none 

 behind. Eyes without footstalks. 



Genus. MUREX. Varices continuous, three or more 

 rows. Aperture rounded, beak mostly very long, canal 

 partly closed. Many seas. 



Genus. TRITON. Varices not continuous ; lips toothed. 

 Warm seas. 



Genus. RANELLA. Two rows of continuous varices. 

 Many warm seas. 



Genus. PYRULA Pear-shaped ; spire short, outer lip 



thin ; canal long and open. Warm seas. 



Genus. FASCIOLARIA. Shell Ions: : canal open. Several 

 oblique folds in inner lip. Warm seus. 



Genus. FDSUS. Shell spindle-shaped, spire short. outo 

 lip thin ; canal lonp and open. Warm seas. 



