82 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY — IV.' 
Subclass CHONDROSTEI. 
{The Sturgeons.) 
Skeleton partly cartilaginous. Ventral fin abdominal, with an entire 
series of basilar segments. No snbopercnlum or preopercnlnm . Branchi- 
ostegals (single or) wanting ; a praicoracoid arch ; no symplectic bone. 
Mesopteryginm distinct ; interclavicles present.* Arterial bulb with 
several pairs of valves. Optic nerves forming a chiasma. Intestine 
with a spiral valve. Air-bladder connected by a dnct with the cesopha- 
gus. Tail heterocercal, its fin with fulcra. Skin naked or armed with 
bony jilates. This group comprises two orders. 
(Order Chondrosfei Gunther, viii, 332-347. ;^;6v4pof, cartilage ; uareov, hone.) 
ANALYSIS OF ORDERS OF CHONDROSTEI. 
* Maxillary and iuteropercle obsolete; shin naked; branchihyals cartilaginous; air- 
bladder cellular Selaciiostomi, G. 
** Maxillary and interojjercle present ; skin 'ATitli bony shields ; branchihyals osseous ; 
air-bladder simple Glaniostomi, H. 
Order G.-SELACIIOSTOIMI. 
{The Faddle-Jishes.) 
A prtecoracoid arch ; no symplectic bone ; premaxillary forming month 
border ; no suboperculum, preoperculum, nor interoperculum ; mesop- 
terygium distinct ; basihyals and superior ceratohyal not ossified ; inter- 
clavicles present; maxillaries obsolete; branchihyals cartilaginous. 
This order contains bnt one family, PoJyodontidcv. {(yt)Ayr,.^ shark ; ffro/jta, 
mouth.) 
Family XXV.— POLYODONTID.^. 
{The Faddle-Jishes.) 
Body fusiform, little coinjiressed, covered with mostly smooth skin. 
Snout prolonged, exj^anded into a thin, flat blade, the inner jiortion 
formed by the produced nasal bones, the outer portion with a reticulate 
bony frame- work, the whole somewhat flexible. Mouth broad, termi- 
nal, but overhung by the spatulate snout, its border formed by the pre- 
maxillaries, the maxillaries being^bsolete. daws with many finedecid- 
* The osteological characters here and elsewhere in this work are mostly taken from 
Cope’s “ Contribution to the Ichthyology of the Lesser Antilles ”. Trans. Am. Phil. 
Soc. 1870. 
