14 



AMERICAN HYDROIDS. 



have also been divided into two general classes, according to their attachment to the hydrocaulus. 

 When joined to the latter by a slender pedicel which admits of more or less movement, they are 

 called free nematophores, and are characteristic of the eleutheroplean plumulariaiis; when they are 

 firmly joined to the hydrocaulus by a broad rigid base they are called fixed nematophores, and 

 are characteristic of the statoplean plumularians. Each of these groups is again divided into 

 mono tli a 1 11 in ic and bithala-miv uematophores, the former name being given to those without an 

 internal circular ridge or shelf partially dividing the interior into two chambers; and the latter 

 name being applied to those forms having this structure. The prevalent type in the Eleuthero- 

 plea is the bithnlaruic, while in the Statoplea the monothalamic nematophore prevails. There are 

 exceptions, however, ill both cases. Plumularia si-mi I is (tig. 47) and Plumitlaria pinnate-, generally 



TYPICAL NEMATOI'IKIRKS UF THE ELEUTHEUOI'LEA. Much enlarged. 



Fig.:n.riumulariame<jaluceiihala. Fig. 44. S. diehotoma, m.'sial. 



Fig. 38. I'.clarkei, mesial. ' Fig. 45. Diplopteron lanyipmuitm, mesial. 



Fig. 39. - Monostcechas qvadrident, cauline. Fig. i6.Polyjilitmtilaria annata, mesial. 



Fig. 40. M. <i>tadridens, supraealyi-iue. Fig. 47. I'lumularia similis. 



Fig. 41. J/. ituadriil-itx, nn-Nial. Fig. 48. Diplopteron qtiadiicorne, slipracalyiue. 



Fig. 42. Ctilmnia mirabilis. Fig. 48.nalopterix carinata, supracalyciue. 



Fig. w.Schiiutricha parvula, mesial. Fig. 50. H. carinata, mesial. 



regarded as eleutheroplean species, have monothalamic nematophores, while Nwditheca dalli 

 (figs. 71, 7-), a statoplean, has plainly bithalamic nematophores. So far as I have been able to 

 ascertain, no American eleutheroplean has monothalamic nematophores. 1 There are also a num- 

 ber of intergradations between the free and fixed nematophores. Indeed the monothalamic 

 nematophores found in the genus I'lnnuihiriu are all "fixed", in a literal way, and such species 

 as P.pinnata and P. similis should probably be placed in Jickeli's genus Kirchenpaueria, as modi- 

 fied by Bale, characterized by an absence of the supracalycine nematophores and the presence of 

 naked sarcostyles in their places. Both P. pinnate and P. similis are possessed of these char- 

 acters and, in addition, their nematophores are monothalamic and fixed, in which they further 



'Since writing the above I have found monothalamic nematophores on a new species, PI ttmidaria goodei, from 

 California. (Seo pi. vn, tig. 4.) 



