iS 



3. Fam. CENTRISCIDAE. 



Physoclists. Body elongate, extremely compressed with scharp 

 ventral edge. Head produced into a long tube with the mouth 

 terminal, small and toothless* Trunk ending posteriorly in a 

 long strong spine with or without a movable spine at its end. 

 Below it are situated 2 dorsal fins, a spinous dorsal, close to 

 the strong spine and a soft one directed downward. The 

 longitudinal axis of the short, movable tail is deflected at an 

 obtuse angle from that of the trunk and terminates in a short 

 caudal. The anal lies close before it. Body for its greater part 

 transparent and^ encased in a dorsal and ventral exoskeletal 

 unflexible cuirass. The former is composed of two alternating 



Fig. 8. Centriscus scutatus L. 



Dorsal cuirass: i 5 upper dorsal row of plates. I v lower lateral row. 

 The line running through those plates corresponds to the 

 inner ridge connected with the vertebral column. 



Ventral cuirass: I 14 ventral plates; 8 with the ventrals. T dorsal spine. 

 (After JUNGERSEN). 



rows of 5 bony plates, each connected by suture. The lower 

 (or lateral) row of plates, across which runs the lateral line, is 

 connected with the vertebral column. Behind the fourth plates 

 of the upper row and wedged in between the fifth plates of 

 that row is situated an unpaired plate covering the base of 

 the terminating strong spine. In Aeoliscus there is another 

 small, unpaired endoskeletal plate anteriorly in the middle line 

 of the back between the posterior ends of the first pair and 

 the anterior ends of the second pair of plates of upper row. 

 The ventral cuirass consists of a row of 13- 15 exoskeletal 

 plates. Anterior 5 6 vertebrae elongated, the transverse pro- 

 cesses of the second to fourth or fifth connected with the 

 dermal plates. In the skull the parietals are wanting; the true 

 mouthparts are small. The prolongation of the snout is pro- 

 duced by the prolonged mandibulary suspensorium and by 

 the praeoperculum developed into a thin, transparent plate, 

 anteriorly attached to the prolonged quadrate. Other opercular 

 bones well developed. The ventrals are abdominal, more or 



