SCIENCE-GOSSIP. 



123 



swimming molluscs, such as the pectens, the mud 

 would have no opportunity of forming and remaining 

 a sufficient length of time to become indurated, i< >r 

 every little accumulation would be washed out by 

 the motion of the shell through the watei 



This Lamellibranch will not survive long in 

 confinement, therefore little can be gleaned of its 

 life-history. When placed in the tank it soon 

 partially buries itself in the mud, and remains in the 

 same spot until death ensues. Its food consists of 

 the minute organisms contained in the element 

 around it. After filling its shell with water it 

 slowly but forcibly ejects it by gradually closing 

 the valves, retaining as the liquid filters out such 

 divers forms of life as its fancy dictates. 



The identity of the fry still remains an open 

 question. Gwyn Jeffreys considered Kelliella abys- 

 sicola to be the young, but many other authors 

 disagree with this, and the point still remains to be 

 proven. I have opened and examined a large 

 number .of individuals, and also carefully washed 

 and strained quantities of the mud in which the 

 animals lived, but never had the good fortune to 

 discover a single baby shell. My want of success 

 may be accounted for by assuming that I did not 

 get the shells during the breeding season, or that 

 when extruded from the parent, the fry are free- 

 swimming creatures, and, not requiring maternal 

 care, ungratefully leave the home of their birth. 

 Still, it is most singular that they should so long 

 have eluded discovery. 



Isocardia cor is well distributed along our western 

 and southern coasts. I have obtained it from 

 Dundrum Bay, the Isle of Man, off the Smalls, 

 Lundy Island, the south and south-west of 

 Ireland, and also from the Bay of Biscay. It has 

 also been taken in the Clyde near Cumbrae, and 

 in several other localities. It must be borne in 

 mind however, that other than the forces of nature 

 have assisted in its distribution. It often happens 

 that a large number of various kinds of shells are 

 brought up in the trawl nets with the fish. After 

 the fish have been picked out the shells are thrown 

 back into the sea at a distance, perhaps, of many 

 miles from the place where they were brought to 

 the surface. The great home of the Isocardia? is 

 undoubtedly the sea around the Isle of Man. Here 

 a well-chosen spot will yield a large number of 

 these shells. The principal form is that ap- 

 proaching the var. quadrata, and very fine specimens 

 are sometimes met with. The largest one I have 

 seen measured eleven and three-quarter inches 

 in girth. 



The shell figured as the type is by far the most 

 prevalent form and also the most widely dis- 

 tributed. It is sub-orbicular and agrees with 

 Sowerby's figure fairly well. The measurements 

 given are taken thus :— length from the anterior to 

 the posterior margin ; breadth, the distance be- 



tween the greatest convexity of the valves ; depth, 

 from the dorsal to the ventral margin 



Var. 1, spharalis. Shellspherical, thick and solid, 

 umbones prominent, widely divergent and 

 nearly even with the anterior edge 



cent., breadth, 8$ cent., depth, 7.-J- cent 

 Habitat, seventy fathoms, Bay of Biscay. 

 This variety differs chiefly from the type in 

 being abnormally broad, exceeding in this 

 respect the length or depth. 



Var. 2, quadrangula. Shell rectangular, some- 

 what coarsely ridged in lines of growth, 

 anterior margin rounded — being almost semi- 

 circular — and projecting much beyond the 

 level of the umbonal curve. Posterior margin 

 truncate and nearly at right angles to the 

 ventral margin, which is almost straight. 

 Length, 8£ cent., breadth, 6-} cent., depth, 04 

 cent. Habitat, thirty to sixtv fathoms, Isle of 

 Man. 



Var. 3, osculum. Shell similar in shape to the 

 last, but with this difference: some distance 

 back from the anterior margin the valves 

 diverge and run horizontally parallel to each 

 other, gaping at the extremity, forming lips as 

 it were ; the extreme width of the opening is 

 5 mms. Length, S£ cent., breadth, 64 cent., 

 depth, 7^ cent. Habitat, Isle of Man. Five 

 specimens. 



Var. 4, quadrata. Shell large, square, somewhat 

 compressed and coarsely ridged in lines of 

 growth. Anterior and posterior margins 

 flattened and almost at right angles to the 

 ventral margin, which is slightly more curved 

 than var. quadrangula. Umbones small, nuclei 

 obtuse. Length, 9^ cent., breadth, 7J cent., 

 depth, S| cent. Habitat, S.W. Ireland. Scarce. 



Var. 5, ovalis. Shell ovate, anterior margin 

 obliquely truncate : posterior margin short, 

 pointed and abruptly sloping downward and 

 backward, forming a graceful oviform curve. 

 Length, 8 cent., breadth, 7 cent., depth, 7^ cent. 

 Habitat, St. Brides Bay. Rare. 



The cause of the gape of var. osculum is doubtful. 

 Mr. Marshall suggests that the aperture was made 

 to extrude some foreign substance which had found 

 its way into the shell. I cannot quite concur in 

 this theory, for in my opinion the animal would 

 have ejected the intrusive substance by the same 

 way that it entered without making a permanent 

 orifice in its shell, which, besides the labour en- 

 tailed would give its enemies an easy chance of 

 getting at it. Assuming that the Isocardia had 

 made this passage for the purpose suggested it 

 would surely close it again, but no indication of 

 such an occurrence existed in any of the shells 

 that I examined, so I think we must look for some 

 other cause for this aperture. I may add that I 

 have dropped substances into the open valves of 

 an Isocardia, but the)- were invariably extruded at 

 the time, and the animal would close its shell and 

 not open it again for a considerable period. 



There are many intermediate forms leading up to 

 the varieties here described, and perhaps a few that 

 slightly differ, but none of the latter are sufficiently 

 distinct to merit a varietal name. 



,|2, Si theby Road, Highbury, N. ; April nth, ; - | 



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