THE COLLECTION OE MISS H. &A.TT£. 147 



of upwards of 6 inclies. Its pinnfB are long, exceeding towards 

 the proximal end of the stem an inch in length. They are further 

 remarkable in being opposite instead of alternate, and present 

 the still more exceptional character of being quite destitute of 

 joints. "While the hydrothecae of the pinnae are alternate, those 

 of the stem are opposite, or nearly so, and are more distant than 

 those of the pinnae. 



The stem is marked along its entire length by prominent 

 longitudinal parallel striae, which present a somewhat interrupted 

 or beaded appearance. These striae are continued along the 

 pinnae, where, however, they are less distinct. Prom the pinnae 

 they are further continued for some distance along the apocauline 

 side of the hydrothecse, giving to these when seen in profile a 

 rugose appearance towards the base. The stem differs from the 

 pinnae iu presenting a few joints at wide and variable intervals. 



Thuiaeia heteromoepha, n. sp. (PL XX. figs. 1-5.) 



Trophosome. — Stems simple, monosiphonic, springing from a 

 plexus of creeping fibres, closely set with regular alternate pinnae, 

 each of which has its proximal internode small, spatulif orm, and 

 destitute of hydrothecae. Internodes of stems carrying each 

 three or four pairs of subopposite hydrothecae, which are nearly 

 cylindrical, with the orifice destitute of teeth and directed obliquely 

 forward, widely separated from one another transversely, and 

 adnate to the internode by the whole of their posterior side. 

 Hydrothecae of pinnae opposite but in other respects variable — two, 

 three, or four pairs being borne by an internode in some pinnae, 

 in others only one ; hydrothecae of every pair on some internodes 

 connate to one another by their opposed sides, in others separate. 



Gonosome not known. 



Locality. Tasmania. 



The species here described is full of significance in its bearing 

 on the question of the definitiveness of systematic characters ; for 

 the disposition and form of the hydrothecae vary in different parts 

 of one and the same colony to an extent which, if noticed in 

 separate colonies, would be regarded as affording grounds for 

 generic distinction. In fact the very characters which are here 

 associated do occur separately in other Sertularian hydroids, and 

 have been made the distinguishing marks of no fewer than three 

 genera, TJiuiaria, Desmoscyphus, and Sertularia. 



The main stem, which attains a height of about an inch and 

 a half, is throughout that of a typical Thuiaria, not only in the 



