NILS ROSÉN, STUDIES ON THE PLECTOGNATHS. 



species the sinus venosus 

 is large and notched bebind. 

 There is only one pair of 

 semilunar valves in the co- 

 nus arteriosus, dextral and 

 sinistral in position. The 

 bulbus arteriosus is very 

 thick and muscular. In D. 

 hystrix there are two hori- 

 zontal auriculo-ventricular 

 valves, respectively anterior 

 and posterior in position. 

 In B. holacanthus I was not 

 able to state the number. 

 Lactophrys (I have dis- 

 sected L. trigoniis L.) has 

 a heart which resembles 

 very much that of the sal- 

 mon. It shows four almost 

 triangulär areas, one dorsal, ^^g 3 Heart of Diodon hystrix L. 



intO which pOSteriorly the (adult). a from the right, b ventral view. 

 , • j £ Reference letters as in Fig. 1. 



atrium opens, and rrom ^ 



which anteriorly the bulbus arises, two lateral and one poste- 

 rio-dorsal. There are two auriculo-ventricular valves, one 

 anterior and one posterior, and one pair of semilunar valves 



^ 



Fig. 4. Heart of Lactophrys trigonus L. a showing the position in tho 

 body; b from behind ; c vertical section. Reference letters as in Fig. 1. 



