Mr. Alder on the Genus Polycera. 



341 



branchia? of about five pectinated branches each, the points of which 

 are tipped with pale yellow. The anterior plume is longest, the 

 two side ones shorter, and all having a graceful curve inwards. Sur- 

 rounding these are ten linear, subclaviform, branchial appendages ; 

 generally arranged five on each side, and tipped with orange or pale 

 yellow. The hinder part of the body tapers to an obtuse point, is 

 slightly keeled, and sometimes marked with an orange central line. 

 The viscera are seen in a brown or pinkish mass through the trans- 

 parent skin. There is no cloak, nor are the sides of the body angu- 

 lated as in the other Polycerce, but gradually rounded off to the foot. 

 Foot linear, narrow, grooved down the centre, and cloven at the 

 hinder extremity. No spicula?. The orifice of the sexual organs on 

 the right side. 



A few specimens of this elegant and graceful little animal 

 were found in pools among the rocks near low-water mark at 

 Cullercoates. 



Occasionally this species is entirely white, the body being 

 semi-transparent and the tips of the appendages opake. The 

 number of branchial appendages varies, one or two of them 

 being sometimes rudimentary or entirely deficient. One in- 

 dividual spawned while confined in a glass of salt water. The 

 spawn was deposited in a single broad gelatinous band form- 

 ing a semicircle, and strongly glued to the side of the glass*. 



The pulsations of the heart varied from 45 to 75. 



The first of the species here described may be considered 

 the type of the genus Polycera. 



The second agrees with it in the prismatic form of the 

 body, and longitudinal rows of tubercles ; in the presence of a 

 veil and of eyes ; but differs in the number and form of the 

 branchial lobes, and in having imbedded spiculae. 



The third has much fewer points of resemblance ; it agrees 

 with the former in general contour, in the presence of tenta- 

 cular filaments and of branchial lobes ; but the prismatic form 

 of the body and the lines of tubercles are no longer seen. 

 The frontal veil and eyes f are also absent, and the branchial 

 lobes, becoming greatly more numerous, completely encircle 

 the plumes J. Taken collectively, these variations from the 



* A specimen of Eolidia rufibranchialis, contained in the same glass, de- 

 posited its spawn in a narrow waved thread, many times convoluted, and 

 forming a pattern something like a true lover's knot. This was in the 

 month of July. 



f In none of the individuals I examined did I observe any appearance 

 of eyes. Since the above was written, however, my friend Dr. Johnston 

 had kindly favoiued me with a drawing and description of a very similar 

 mollusk discovered by him at Holy Island, in which he observed two 

 "very minute eyes." I must therefore admit the possibility of my having 

 overlooked these obscure organs. 



X The whole three species a«ree in all the characters of the genus given 

 by Rang, with the exception of the tentacula being " contractiles dans une- 

 cavite a character not to be found in any of the British species. 



