River Sturgeons of the American Genus Scaphirhynchus: Characters, Distribution, and Synonymy

Home Browse Search

170 Bailey and Cross are carinate. A small plate at the anterior end of the ventrolateral row is tallied, even if it is not keeled, as long as it is cle:irly an ele- ment in this series. In the dorsal and anal fin -ray counts if . , L, rior rudiments behind the predorsal and preanal plates are included. The last ray in those fins, as counted, is double at its base. The pectoral count includes the strong spine anteriorly and all posterior rudiments (these may be tiny, and an appreciable personal error is involved in counting unstained material). The pelvic count includes all rudiments anteriorly. In all fins the rays are closeh- s =.,(1, and accurate counts require patience, good illumination, and considerable magnification; they usually entail preparatory removal of superficial tissue by scraping. L se of insect pins to mark out sectional counts help- to eliminate errors. the standard length terminates at the posterior end of the last carinate plate of the lateral series (this point is treated as the base of the caudal fin). The origin of the dorsal and anal fins is .,.1:, ., as the posterior edge of the predorsal and preanal plates : "tile large, noncarinate plates lying just in front of these fins). Body width is measured at the shoulder girdle. Caudal - peduncle depth and width are taken at the plane of the least depth. Head length is measured to the posterior (bony) margin of the primary bone of the Omer ^nlum, which in sturgeons is the 41bopercle (the opercular r. is commonly curled under, and to include it introduces an er r). Head depth is the vertical measurement from the top of the left parietal crest. Head width is the maximum breadth of the rostrum. Rostral length is taken from snout tip to the prominent angle of the suborbital. The orbital length is established visually. Nostril width is the greatest dimension of each nostril. „ +h width is the greatest overall extent of the lips. Measm- r., .- volving barbels are taken from the anterior edge of their baoes; the lengths are taken on both barbels of a pair and the longer is recorded. The front of the mouth is that point on the mid -line that lies on the anterior, cartilaginous edge of the labial depression. Caudal -fin measurements are taken from the fin base (see definition of standard Ie!,:rth above); the filament is included, but since this s,.., .•t !r;. ' commonly broken the measurement is minimal. The U. the tenth Iateral plate is taken, and the distance from the lower edge of this scute to the closest plate in the ventrolateral series is used as the interspace between these rows of plates.