3140 Bulletin 4.7, United States National Museum. 



spots, while others have few or none. The young have no spots. Our 

 specimens vary in length from 10 to 60 centimeters. 



Istlarins balsanus has a large and rather complex air bladder. It lies 

 close to the spinal column and extends almost to the posterior end of the 

 body cavity. It is divided by a deep transverse constriction into two 

 halves. The anterior part is heart-shaped, constricted dorso-ventrally. 

 It is separated by a T-shaped partition into 3 chambers. Of these the 

 anterior, transverse chamber is partly divided on the median line by a 

 fold of the dorsal wall of the bladder over the vertebral column. The 

 transverse chamber is connected on each side with the 2 posterior lateral 

 chambers by large openings in the ends of the transverse wall. The 

 posterior half of the bladder is without partitions. It is connected with 

 the left lateral chamber only by a small opening. (Jordan & Snyder.) 



Known only from Rio Ixtla at Puente de Ixtla, Morelos, Mexico. (Type, 

 No. 6149, L. S. Jr. Univ. Mus. Coll. Jordan & Snyder.) 



Istlanus balsanus, JORDAN & SNYDER, Bull. TL S. Fish Com. 1899 (1900), 118, Rio Ixtla, 

 Morelos, Mexico. 



Page 211. After Algansea tincella (Cuvier & Valenciennes), insert: 

 337 (b). ALGAXSEA LACUSTRIS, Steindachner. 



Head 3.67; depth 5; eye 4. 75; snout 3.6; interorbital 3. D. Ill, 7; A. 

 iii, 6; P. 17; V. 9; scales 76-13. Body elongate, strongly compressed be- 

 hind ; caudal peduncle long and slender, its length 5 in head, its depth 10; 

 head pointed, rounded above, greatly increasing in width behind the eyes 

 where the width is half the head's length ; mouth slightly oblique, jaws 

 equal; tip of chin slightly thickened; maxillary nearly reaching eye; 

 gape 4 in head ; preorbital boat-shaped, concave above, convex below, 

 equal to eye, or 1.6 longer than wide; teeth 4-4, hooked, with compressed 

 crowns. Origin of dorsal midway between anterior border of eye and 

 base of caudal, a little in front of ventrals, whose origin is equally dis- 

 tant between center of eye and base of caudal; height of dorsal 1.75 in 

 head, its base half its height; height of anal 2.14 in head, or twice its 

 base; caudal forked, 1.2 in head, the middle rays not quite half length 

 of longest; ventrals short, 2.17 in head, their tips not reaching vent; pec- 

 toral 1.6 in head. Scales firm, half-oval in shape, larger posteriorly; 

 lateral line on middle of side, descending somewhat anteriorly. Color 

 dark brownish gray above, a darker band along middle of side; color 

 below lateral line becoming abruptly lighter gray, merging into silvery 

 on under parts. One example 20 cm. long from Lake Patzcuaro, Mexico. 

 (Steindachner.) 



Algansea lacustri.i, STEINDACHNER, Einige Fischarten Mex., 10, pi. in, figs. 1-1 &, 1895, Lake 

 Patzcuaro, Mexico. (Coll. Princess Theresa von Bayern.) 



Page 254. Orcella, proposed by us for a subgenus in Xolropis, is pre- 

 occupied by Orcella, Gray, 1866, a genus of Cetacea. For our use of it we 

 substitute Orcula. 

 Orcula, JORDAN & EVERMANN, new subgenus in Notropis (orca). 



