1891.] NATURAL SCIENCES OF PHILADELPHIA. 471 



NEW AND HITHERTO TJNFIGTJRED JAPANESE MOLLUSKS. 

 BY H. A. PILSBPvY. 



The forms noticed below, and illustrated upon the accompanying 

 plates, were collected in Japan by Mr. Frederick Stearns, of Detroit, 

 Michigan, and placed in the writer's hands for study. So rich in 

 animal life are the Japanese waters, that we may still expect novel 

 and beautiful forms of mollusks for many years to come, from that 

 quarter. 



The illustrations are due to the liberality of Mr. Stearns. 



Thylacodes medusae n. sp. PL XVII, XVIII. 



A large species, nearly always living in clusters, attached gener- 

 ally to shells. The young form an irregular spiral, the whorls of 

 which rest prone upon the base of attachment. As the tube increases 

 in diameter it becomes carinated on the lower outer portion, or the 

 part corresponding to the " shoulder " of the whorl in a regularly 

 spiral gasteropod. At this stage the whorls become more laxly 

 coiled, and when not too closely clustered, present the appearance of 

 such planorboid forms as T. master Dh., T, atra Rouss, etc. This 

 stage is shown in the cluster pictured on pi. XVI. The subsequent 

 growth is erect and but slightly spiral, the tube generally contracting 

 slightly in diameter, and cylindrical in form. The sculpture consists 

 of narrow longitudinal cords at rather wide intervals, the spaces 

 being occupied by a variable number of threads, (usually three) of 

 which the middle one is larger. Irregular growth-lines crenulate 

 the longitudinals. This sculpture is normally developed upon all 

 sides of the tube. Upon the latter part of the free portion it is often 

 subobsolete. 



The aperture is circular in adult shells, at right angles to the tube, 

 and white within. The external surface is of a pale brown tint. 



No internal septa were found in numerous broken specimens ; and 

 although the shells were apparently alive when collected, no oper- 

 cula were preserved in them, the absence of this organ being one of 

 the characteristics of Thylacodes. 



The dimensions may be seen in the figures, which are of natural 

 size. The diameter of the tubes at the aperture averages 13 mm. 



The embryonic shell, at the time it becomes attached, is bulimiform, 

 glossy and smooth ; lying upon its side. The first whorl formed 



