1886.] NATURAL SCIENCES OP PHILADELPHIA, 241 



cc. Sides with 2 to 6 bony dermal plates ; caudal peduncle 

 keeled or not. 

 d. Yentral spine without cusp at base, 

 e. Dermal plates 4 to 6 ; body stout, little compi'essed ; head 

 large, flat above, a small knob at occiput. Mouth large, 

 maxillary almost reaching front of orbit. Teeth in broad 

 bands in front. From occiput, two rows of mucous pores 

 diverge to posterior borders of eye, extending thence 

 parallel with the orbit to above nasal opening forming an 

 arrow-shaped figure. Plates on sides imbedded, thin; 

 striate ; the last one immediately in front of second dor- 

 sal spine. Post-pectoral plate striate j^-shaped. Scapula 

 forming a striate post-opercular plate. Caudal peduncle 

 very thick to a point immediately in front of caudal 

 where it is much compressed. Innominate bones and 

 ventrals vaiying much in relative length, so that in some 

 specimens the one is the longer in others the other. 

 Dorsal spines short, straight, broad at base, serrate on 

 outer edges. First spine about f in eye, third very 

 small. Caudal slightly lunate. Anal inserted under 

 fifth dorsal ra}^, coterminous with the dorsal. Yentrals 

 coarsely serrate on outer and finely on inner edges. 

 Pectorals broad and short, fan-shaped. D. I-I-I, 11 to 

 13 ; A. 1, 9. Olivaceous, silvery below, thickly punctu- 

 late. MicROCEPHALUS. 5. 



ee. Dermal plates on side 2 or 3, strong, not imbedded. Mouth 

 large, maxillary reaching to below front of orbit. Mu- 

 cous pores none. Scapula forming a post-opercular plate. 

 All bones thicker and stronger than in micr^ocephalus. 

 Caudal peduncle compressed for its whole length. 

 D. I-I-I, 10 to 12 ; A. 1, 8. Wheatlandi. 6. 



dd. Ventral spines each with a distinct cusp at base. Lower jaw 

 the longer. Teeth in lower jaw stronger than in upper. 

 Diameter of orbit 3^ in head. Sides with 1 plates. In- 

 nominate bones almost reaching vent. Caudal peduncle 

 with a membranous carina. Caudal fin forked. Ventral 

 ^ in. finely serrate. Pectoral j in. Length of specimen 

 2^. D. I-I-I, 12 ; A. 1, 8. Uniformly grayish on back, 

 head and posterior halfof body ; abdomen yellowish. 



DiMIDIATUS. 7. 



