20 VROCEEBINGS OF THE MALACOLOGICAL SOCIETY. 



ON THE ANATOMY OF EPHIFFODONTA MACDOUGALLI, TATE. 



By M. r. Woodward, Demonstrator of Zoology, Royal College of 



Science, London. 



Read July lith, 1893. 



PLATE II. 



OwTNc. to the kindness of Mr. E. R. Sykes, I have had placed at my 

 disposal a niimbcr of specimens of a very interesting lamcllibranch, 

 viz. : — Apliippodonta MacDougalli, Tate. 



In his original description' the founder of this genus enumerates 

 briefly the leading external characters of the animal and its shell, but 

 makes no attempt to deal with its detailed anatomy, and further, as 

 one or two points which he describes in its external features arc 

 inaccurate, I have thought it worth while to place on record a more 

 detailed account based on the careful dissection of two specimens and 

 on two complete series of transverse sections of decalcified specimens 

 examined microscopically. The largest specimen measured 11mm. 

 long, the smallest 7mm. 



The Shell presents one or two interesting features which have not 

 yet been described. One of the most striking may be noticed on holding 

 the valves up to the light, when it will be seen that their structure 

 is like a lattice-work, being made up of a series of strong radiating 

 costa3 and of slighter circumferential bands, the interspaces being 

 extremely thin and transparent, so much so that in decalcified sections 

 the shell seems in places to be almost wanting.^ The numerous series 

 of conspicuous spines are attached to the costae. 



Vertical sections of the dried shell show that it is entirely devoid of 

 periostraciim, and also of any prismatic layer, unless the radiating lines 

 (Fig. 18, /. I.) observable in the spines arc to be so interpreted ; these 

 lines have, however, much more the appearance of radiating tubules, 

 especially in the thinner decalcified section, and such I take them to 

 be ; they seem moreover to communicate with a central cavity in each 

 spine. The main mass of the shell appears to be made up of lamellas 

 deposited parallel to the surface of the shell and apparently represent- 

 ing the nacreous layer (Fig. 18, n. I.). 



The absence of the periostracum is another point of resemblance, 

 in addition to those enumerated by Tate, between this form and 

 Scintilla.'^ 



The organic basis of the shell is very slight, and in section 

 the shell has the appearance of a series of spines united by a 

 mere strand of conchiolin. 



An internal ligament is present as in Galeomma. 



1 Trans. Roy. Soc. S. Aust. xi. 1889, p. 63 and xiv. p. 267. 



^ It is interesting to note that in Scintilla the shell may be finely perforated. 



3 Deshayes, I'roc. Zool. Soc. 1855. p. 171. 



