GENUS ACINETA. 829 



cule subspheroidal or pyriform, rarely occupying more than the anterior 

 moiety of the lorica ; tentacles distinctly capitate, forming a single anteriorly 

 developed sheaf or fascicle, their length when extended equal to that of 

 the body ; contractile vesicle single, lateral ; endoplast unobserved. Length 

 of lorica 1300". 



HAB. Salt water, on various Hydroid zoophytes, seaweeds, and 

 Polyzoa. 



The distribution of this species, figured and described by M. C. Mereschkowsky 

 in the 'Annals and Magazine of Natural History ' for March 1881, is not, as its title 

 would imply, limited to the Livadian seaboard. So long since as July 1879 the 

 author obtained it in abundance attached to zoophytes and Polyzoa collected on the 

 coasts of Devonshire and Cornwall, and more recently, August 1881, from the 

 Menai Straits, North Wales, growing in company with Adneta tuberosa and 

 Ophryodendron sertularia on Sertularia abietina. The symmetrically ovate 

 contour of the lorica distinguishes it readily from any of the species previously 

 described. 



Acineta tuberosa, Ehr. PL. XLVIII. FIGS. 25-28 AND PL. XLVIIlA. FIG. 7. 



Lorica compressed, subtriangular, widest at its distal margin, and 

 thence tapering gradually towards its point of junction with the pedicle, the 

 lateral walls continuous over the frontal border, leaving two ovate apertures 

 at the anterior angles for the extrusion of the tentacles ; pedicle slender, 

 rectilinear, varying from equal to, to as much as four or five times the 

 length of the lorica ; body of animalcule mostly attenuate posteriorly, 

 rarely filling the cavity of the lorica except towards the anterior border* 

 invariably adherent to it by its posterior extremity, in the region of the 

 tentacles, and usually along four perpendicular lines extending from the 

 posterior extremity towards the anterior border, such lines of adhesion 

 communicating to the body as seen in vertical optic section a distinct 

 quadrilateral contour; tentacles forming two antero-lateral fascicles, pro- 

 truding when extended through the corresponding ovate apertures in the 

 lorica, withdrawn in a sheaf-like manner into the substance of the body by 

 invagination when retracted ; contractile vesicle single, anteriorly located ; 

 endoplast elongate-ovate or cord-like, often contorted and branched. 

 Length of lorica 1-500" to 1-300". HAB. Salt water. 



The synonymy of this species has become somewhat involved in consequence 

 of its close resemblance to a fresh-water type, originally connected with the same 

 title by Stein,* and which is here held to be identical with the Acineta lemnarum 

 of the last-named investigator. The species first distinguished by the title of Acineta 

 tuberosa by Ehrenberg, is essentially a salt-water form, having a cosmopolitan 

 distribution, and although but imperfectly figured and described by that authority, 

 the attention bestowed upon it by several more recent investigators has resulted in 

 the elucidation of almost every important structural detail. In this connection, 

 attention may be more especially directed to the elaborate account and illustrations 

 given of it by M. Julien Fraipont in his memoir upon the Acinetidae of the coast 

 of Ostend.f As indicated by this authority, the essential difference subsisting 



* 'Die Infusionsthiere,' pi. Hi. figs. 48-50, 1854. 



t ' Bulletins de 1' Academic Royale des Sciences de Belgique,' 1878. 



