Limitation of Genera among the Hydroida. 367 



cemiform peduncles, which spring from the body of the polypite 

 between the proximal and distal verticil of tentacles. 



The genus Tubularia of modern authors has been broken up by 

 Agassiz into four separate genera, for one of which he retains the 

 older name Tubularia, while he designates the three others respect- 

 ively Parypha, Thamnocnidia, and Ectopleura (Cent. Nat. Hist. 

 U. S. vol. iv.). He gives no technical diagnosis 'of any of these 

 genera ; but, from my own knowledge of the European species which 

 he separates from Tubularia, as well as from the very detailed 

 descriptions and beautiful figures of the American species which he 

 now for the first time describes and refers to his new genera, I can 

 find only in one of these forms (namely, the Tubularia Bumortieri 

 of Van Beneden) characters which would, in my opinion, justify the 

 proposed dismemberment. For Tubularia Bumortieri Agassiz con- 

 stitutes a new genus under the name of Ectopleura, and in this I 

 willingly follow him ; but the only character of importance by which 

 Parypha and Thamnocnidia are separated from Tubularia is the 

 non-development of gastro-vascular canals in the sporosacs of the 

 species referred by Agassiz to these genera, while they are found in 

 the sporosac of Tubularia indivisa. 



Now I cannot admit that the presence or absence of these canals 

 in a sporosac, so long as they do not bring with them the develop- 

 ment of an open contractile umbrella capable, when detached, of 

 acting as a swimming-organ, can be regarded as affording a character 

 of generic value, even though we leave out of view the great difficulty 

 of detecting it, which is a practical rather than a scientific objection. 



Again, between Parypha and Thamnocnidia the only difference 

 alleged is in the structure of the tentacula-like tubercles which occur 

 upon the summit of the sporosac. I believe, however, that there is 

 here no important difference. I have carefully examined the sporo- 

 sacs of Tubularia coronata, Abildg., a species which Agassiz refers 

 to his genus Thamnocnidia, and 1 can find no essential difference 

 between the tentacular tubercles which crown the sporosac in this 

 species and those described by Agassiz as characteristic of his genus 

 Parypha. 



Tubularia indivisa, Linn., = Tubularia calamaris, Pallas. 



Tubularia Couthoyi, Agass. 



Tubularia coronata, Abild., = ? Tubularia graciliSy Harvey, = 

 Thamnocnidia coronata, Agass. 



Tubularia spectabilis, Agass. (sp.), = Thamnocnidia spectabilis, 

 Agass. 



Tubularia tenella, Agass. (sp.), = Thamnocnidia tenella, Agass. 



Tubularia cristata, M.'Craidy, = Parypha cristata, Agass. 



Tubularia crocea, Agass. {%^.),=i Parypha crocea, Agass. 



Tubularia bellis, Allm. 



Tubularia attenuata, Allm. 



Thbularia larynx, Ellis & Soland. 



Tubularia simplex, Alder. 

 "? Tubularia calamaris, Van Ben. 



