6 JOURNAL OF THE [January, 



The radula of Sycotypus is so large that it is easily obtained by 

 dissection. The following method was employed in the present 

 instances. The living animal was dropped into boiling water, 

 and allowed to remain there for five minutes. A steel fork was 

 thrust into the muscular foot, and a forward, spiral, oscillating 

 motion soon extracted the animal from its shell. The viscera 

 being discarded, the mantle was slit backward along its upper 

 region, disclosing the head, and the remaining mass was divided 

 by a longitudinal incision through the great muscular foot, 

 slightly at one side of the median line, disclosing, but leaving 

 intact, the proboscis. Then by inserting one point of the dis- 

 secting scissors into the oral aperture, feeling the radula so as to 

 be certain the instrument was lying upon, and avoiding all risk 

 of injuring the desired organ, the proboscis was slit along its 

 entire upper surface. The radula was then easily seen, seized 

 with a forceps, and dissected out as far as could be followed. 



As far as I have been able to ascertain the radular sack of 

 Sycotypus continues inwardly for a length at least equal to that 

 of the radula itself, until it becomes an attenuated thread, dips 

 downwards and forwards in several loops, and has its origin 

 underneath and near the junction of the proboscis with the foot. 

 The specimens examined died with the radula bent over the for- 

 ward end of the skeleton, continuing backward and underneath 

 for varying distances, such as i, i, i or i^ths of an inch. 

 The specimens of radula here exhibited were cut into lengths of 

 fths of an inch, flattened by soaking in alcohol while com- 

 pressed between two pieces of glass, and mounted in glycerine. 

 Under the first microscope is exhibited the central portion of 

 the radula of Sycotypus, by polarized light, the teeth being in 

 perfect condition, and giving strong contrasts of colors. There 

 are three teeth in each row. Each tooth consists of a trans- 

 versely extended plate, supporting several denticles. The cen- 

 tral tooth has three denticles, and each lateral tooth has four, 

 with sometimes an additional rudimental fifth denticle. 



Under the second microscope is exhibited the distal end of 

 the radula, where it will be observed the membrane itself 'is rag- 

 ged, and the teeth sometimes entirely dislodged, and when re- 

 maining having the points broken and worn from hard usage. 



Under the third microscope is exhibited the proximal end of 

 the radula. The teeth gradually become smaller and fainter, 



