A EEVISION OF THE BRANOHIOSTOMID.^^. 805 



laterad groups, the ventrad groups distinguished by a very high 

 web. 



2. A caudal expansion of the median dorsal and ventral fin- 

 ridge present or absent. 



3. An unsegmented '^urostyloid " caudal region, one seventh 

 the length of the whole animal, present, or per contra 

 only a minute projection of the notochord beyond the last 

 myotome. 



4. A single, or per contra a double post-atrioporal caecum 

 to the atrial chamber. 



5. Only the right, or per contra both metapleura continuous 

 with the ventral portion of the snout or rostral fin. 



6. The prseoral gustatory groove (groove of Hatschek) super- 

 ficial and shallow, or per contra strongly marked. 



7. Fin-ray spaces present or per contra absent in the median 

 ventral fin. 



8. Fin-rays developed in the fin -ray spaces of the median 

 ventral fin, or per contra absent. 



9. Right metapleur terminating behind the atriopore simi- 

 larly to the left metapleur; median ventral fin unconnected 

 w^ith metapleura ; or per contra right metapleur continued 

 without break into the median ventral fin, 



thus, its posterior continuation. 



10. Number of tentacles to the oral sphincter (intra-buccal 

 cirrhi) twelve, ten, or sixteen. 



11. Gonads developed on both sides of the body, or per 

 contra only on one side. 



12. Number of myotomes throughout the body ; number of 

 myotomes between snout and atriopore, atriopore and anus, 



[N.B. — In counting the myotomes I have reckoned that 

 coincident with the atriopore as belonging to the anterior or 

 prseatrioporal group ; and similarly I have reckoned the post- 

 anal group as commencing behind the posterior margin of the 

 anus. In many specimens the anus is elongated antero- 

 posteriorly, so as to extend under as many as three separate 

 myotomes.] 



13. Proportional height of the median fin. 



