WRIGHTIA. 299 



GONOSOME. — Spokosacs springing directly from the sides of tlic liydro- 

 caulus. 



An important modification of Ehrenberg's genus Eudendrhnn, or rather of Van Bcneden's 

 amended form of this genus, was proposed some years ago by Dr. Strcthiil Wright, who drew 

 attention to the existence in the genus as then generally accepted of two forms of hydranth, 

 which he rightly considered as sufficiently distinct to justify the disuiembernient of the genus. 



In accordance with this view he instituted his genus Atradylis for such forms of the older 

 genus as are characterised by a fusiform shape of the hydranth and a conical hypostome ; the 

 greater number of these species, moreover, presenting a more or less complete retractihty within the 

 suuunit of the hydrocaulus, though nothing like a projjcr hydrotheca is ever developed. 



The forms, however, which Dr. Wright included under his genus Atrarli/Us presented two 

 generic types. One of these had already been characterised under the name of Periyonimus by 

 Sars, who described both the trophosome and gonosome ; ' while another had, under the name of 

 Bougainvillia, been long ago described by Lesson, who, however, was acquainted only with the 

 medusa.^ That the Bougainvillia of Lesson is the medusa of a hydroid whose type is found in the 

 Eudendrium ramosum of Van Beneden ( = Alradylis ramosa of Wright), has been shown both 

 by Wright and Agassiz. To this hydroid and its allied species the name of Bougainvillia must 

 accordingly be restored, and indeed we find Agassiz already arranging such forms partly under 

 Lesson's name and partly under ]S[argelis, Steeustrup's name for a medusa which can scarcely 

 be regarded as distinct from Bougainvillia. 



Some time afterwards a third form, distinct from both Perigonimiis and Bougainvillia, obtained 

 admission into Wright's genus Atractylis. This was the Afracfglis arenosa of Alder, a form 

 which, unlike Perigonimus and Bougainvillia, was now for the first time made known. 



To Alder's Alradylis arenosa, which has been accepted by Wright as a genuine Atradylis, 

 it would therefore be necessary to restrict the name Atradylis, if this name could under any 

 circumstances be retained by the zoologist. Unfortunately, however, Atradylis cannot be 

 admitted as the name of a zoological genus, for it had been long ago appropriated by the botanist, 

 being an old Linnsean name for a genus of composite plants. 



There is thus no alternative but to assign to Atradylis arenosa some other generic name, 

 and that of Wrightia naturally suggests itself, as commemorating the labours of an original and 

 able observer of the Hydroida.' 



' Sars, ' Faun. lit. Norv.' 



"• Lesson, in 'Ann. des Sci. Nat./ v, 1836. 



' The name of Wrightia had been already employed by Agassiz as a generic designation for 

 certain campanulariau hydroids. The forms, however, which Agassiz would include under his genus 

 llric/tttia had been previously assigned by Van Beneden and Hincks to two new generic groups, under 

 the names of Campanulina, Van Ben., and Calycella, Hincks. The IVrightia oi Agassiz must therefore 

 be suppressed in favour of the previously instituted genera of Van Beneden and Hincks. Mr. Alex. 

 Agassiz has indeed already rejected the name of Wrightia, on the grounds that the forms to which 

 Prof. Agassiz had applied it had been previously named. (See ' Hlustr. Catal. N. A. Acal.,' p. 71.) 



39 



