350 BULLETIN OF THE 



appearance. If the function of the organ be still denied by some sceptic who 

 will not be satisfied until the animals have been observed in copula, it remains 

 that, whatever its function, here is an organ unknown in the great majority of 

 Rhiphidoglossa, but which appears in a few diverse deep-water forms. 



These interesting facts were made known by me to Prof. Verrill, Dr. Jeffreys, 

 and others interested, in the early part of 1882. Subsequently, the same organ 

 was observed in Addisonia, and, while closing up my work on this Report, 

 an examination of a male Bimula (Cranopsis) asturiana Fischer added it to 

 the list, still later enlarged by species of Margarita and Turcicula. 



These results show very clearly how much there is still to learn about the 

 macroscopic anatomy of even ordinary mollusks; how little ground there is for 

 dogmatism in the larger features of classification ; and how rich a field is open 

 to the conscientious student who may have access to the sea. 



The old idea, still delusively cherished by most embryologists, that the char- 

 acteristics of a single species may serve to marshal a host of others in line, was 

 always false, and every year shows its falsity more clearly. 



The marshalling must be allowed for convenience' sake, but the idea that it 

 is in any proper sense a finality should be discouraged by every teacher. If it 

 had not been taken for granted these many years, who can doubt that we should 

 long since have known exactly about a hundred species of mollusks where we 

 now have the facts about one or two, and that our classifications would have 

 been ameliorated in proportion ? 



This species must be very abundant in the North Atlantic, as Dr. Jeffreys 

 has informed me that he has examined over four hundred specimens. 



One feature which is often noticeable on the sedentary deep-sea shells, and 

 especially on the limpets, is perhaps worth mentioning. A sort of spongy 

 organism, apparently a sponge or a hydractinian, often covers the upper surface 

 with a coating of fine straight spinules, which appear to be attached to the 

 shell but are easily removed by wetting and rubbing. They are very abundant 

 on Terebratulina Cailkti and other sculptured brachiopods, and I have observed 

 them on all the species of Gocculi-na and on Lepetella. Dr. Jeffreys states that 

 the spinules are not soluble in potash. There has been no distinct outer 

 crust, nor any particular shape, to the aggregations of this sort which have 

 come under my notice, but they seem to be preferably attached to prominences 

 of the sculpture, and might easily be mistaken, in some cases, for part of the 

 shell itself. 



This Cocculina has fine sharp spines, properly belonging to the shell ; but 

 among those in the Jeffreys collection I have seen none quite- as sharp and 

 long as those in the magnified figure (la) of th'e plate to Dr. Jeffreys's paper 

 on the Triton mollusks. 



The section Caccopygia, to which 1 have referred this species, probably in- 

 cludes C. angulata Watson, and other species which have not yet been critically 

 examined with regard to the epipodial filaments. 



