INTRODUCTION. 1XV 



this division. Amongst the Thecaphora, on the contrary, 

 they exhibit very little variation, and the tentacles are in- 

 variably filiform and arranged in a single wreath. A like 

 uniformity prevails in the position of the gonophores 

 throughout the latter suborder; they are always borne 

 on a columnar offshoot from the coeuosarc, which is homo- 

 logous with the proliferous polypite amongst the Athecata, 

 whether fully developed or more or less atrophied. 



The Thecaphora are remarkable for their plant-like 

 growth and the elegance of their forms. * 



The following Table exhibits the scheme of classification 

 adopted in the present work : 



Subkingdom CCELENTERATA, Frey & Leuckartf. 



Class HYUROZOA, Huxley. 

 Ord. I. HYDKOIDA. Ord. II. SIPHONOPHORA. Ord. III. DISCOPIIORA. 



Order I. HYDEOIDA. 



Suborder I. A THE CAT A. 



Hydroida destitute of true thecse or protective cases, either for 

 the polypites or g-onophores. 



Family I. Clavidse. 



CLAVA, Gmelin. 

 TUBICLAVA, Allman. 



TURRIS, Lesson. 

 CORDYLOPHORA, Allnian. 



* These two suborders correspond with the Gymnogonial and Angiogoniul 

 divisions of Allman. The terms here employed seem to me to have tin's 

 advantage, that they are more general in their application, and may be taken 

 to apply both to the trophosorue and the gonosorne. 



t Beitrage zur Kenntn. dcr wirbellosen Thicrc, von Frey u. Leuckart, p. 37. 



