8 LEPTOCARDII: CIRROSTOMI, —I. 
Ciass C.—LEPTOCARDII. (THE LANCELETS.) 
Skeleton membrano-cartilaginous; no brain; no skull; the noto- 
chord persistent and extending to front of body; no heart, its place 
being taken by pulsating sinuses; blood colorless; respiratory cav- 
ity confluent with cavity of abdomen ; gill slits in great number ; 
the water expelled from an abdominal pore in front of vent; no 
jaws; the mouth inferior, slit-like, with cirri on each side. (Gr. 
Aerrés, thin ; xapdia, heart.) 
OrpverR I. CIRROSTOMI. 
The single order of this class contains but a single family. (Lat., 
cirrus, hair; Gr. orca, mouth.) 
Famity I. BRANCHIOSTOMATIDA. (THE 
LANCELETS.) 
Body elongate-lanceolate, compressed, naked, colorless, the fins 
represented by a low fold which extends along the back around 
the tail, past the vent, to the abdominal pore; eye rudimentary ; 
liver a blind sac of the simple intestine. One genus, with 5 or 
6 species; small, translucent creatures found imbedded in the 
sand on warm coasts. These animals are highly interesting to 
the anatomist as showing the vertebrate type in its simplest 
condition. 
1. BRANCHIOSTOMA Costa. (Amphiorus Yarrell.) 
(Bpayxua, gills; oréua, mouth.) 
1. B. caribzeum Sundevall. Lancextet. Muscular bands 
(myocommas) 55 to 60 (87-+14-++ 9 = 60); tail short; extremi- 
ties attenuate. (Otherwise as in the European B. lanceolatum, 
which has 56 to 60 myocommas; 35 + 12+ 13= 60). N.Y. to 
S. A. buried in soft sand, locally abundant. (Name from Carib- 
bean Sea.) 
