254 CEYLON PEARL OYSTER REPORT. 



Panthalis melanonotus, Grube Plate I., figs. 21 to 27. 



Grube, ' Ann. Semp.,' 1878, p. 48 ; also Part I., ' Ceylon Pearl Oyster Report,' p. 71. 



Locality : Station LIV., south of Rameswaram, 40 fathoms. One specimen. 



A typical cirrus-bearing parapodium from the anterior region has the following 

 structure : (i.) A short dorsal cirrus consisting of a stout basal portion and an 

 acuminate apical portion ; (ii.) the dorsal ramus supported by a flexible acicula and 

 penetrated by the tomentose seta? which are employed in weaving the tube ; (iii.) the 

 ventral ramus with four kinds of setae, dorsally a small bundle of very fine serrulate 

 seta?, then a bundle of long delicate penicillate setse, then a central group of stout so- 

 called aristate setse ; lastly, a ventral bundle of long spinulose setae (Plate II., figs. 24 

 to 27). At the tip of the aristate setae there is an alveolus. From the 28th segment 

 the peduncle upon which the dorsal cirrus is inserted acquires a geniculate appendix, 

 containing a prolongation of the internal tissues, possibly a diverticulum of the gut, 

 but of this I cannot be certain without transverse sections. A few segments farther 

 back an ovate or subcylindrical appendix appears on the squamiferous segments, in 

 the same position as that occupied by the cirriform branchia of the Sigalionidae, also 

 containing the same kind of tissue as that which occurs in the geniculate process 

 above described. The surface of these processes is not ciliated (Plate I., figs. 22 

 and 23). 



Panthalis melanonotus appears to be an Indo-Pacific representative of the Mediter- 

 ranean and Atlantic P. oerstedi. The accounts given of the eyes of the latter are 

 rather puzzling. Von Marenzeller* denies the existence of eyes, although the 

 ocular peduncles are present. Mr. Watson, in the article referred to above, has 

 omitted to note the presence or absence of black pigment, t stating that the sight of 

 the animal is good, each reddish-coloured eyestalk being faced with a clear lens, and 

 having at its tip a rounded papillated appearance. 



In Panthalis melanonotus the stalked eyes are very large and provided with 

 abundant black pigment, in the centre of which is a lens ; the eyes are subspherical, 

 occupying the extremity of the clavate peduncles. In addition there is, as described 

 by Grube, an eye-spot on each side of the prostomium behind the ocular peduncle ; 

 between and slightly behind the sessile eye-spots the median tentacle arises. The 

 antennae are small and largely concealed by the eye-stalks and were not seen by 

 Grube (Plate I., fig. 21). 



The extruded pharynx bears distally thirteen papillae above and the same number 

 below, forming a terminal crown ; the median dorsal papilla is enlarged and the 

 median ventral is lost from the specimen. The palps show pigment spots and appear 

 glabrous with a simple lens, although minute papillae can be found with the microscope, 

 especially towards the apex, but there is no marked distinction between apical and 



* V. Marenzeller, 'Polychseten des Grundes,' Vienna, 1893, p. 28. 



t Mr. Watson informs me that no black pigment is visible in the eyes of the specimens of P. cerstedi 

 now in his possession. W. A. Herdman. 



