802 Roijal Society, 



2. Spharia lanci/ormis, Fr., and Hendersonia polycystis, B. & Br. 

 Irregularity of form in the sporidia of Sphceria lanciformis. The 

 growth of perithecia in the same stroma, some producing the fruit of 

 Sphceria lancijbrmisy others that oi Hendersonia polycystis. Notice 

 of the prohahle existence of a third form of fruit of SphcBria lanci- 

 formis. 



3. Sphceria siparia, B. & Br., and. Prosthemium betulinum, Kunze. 

 Constant association of the two forms ; their external resemblance ; 

 nature of the fruit and other circumstances leading to the conclusion 

 of the identity of the two plants. 



"On the Anatomy of Tridacna." By John Denis Macdonald, 

 Esq., Assistant-Surgeon R.N. 



The author first explains the peculiar position which the animal 

 of Tridacna occupies in its shell, in which it differs from bivalves in 

 general. He then describes the mantle and its borders, the mem- 

 branous interpallial septum, the respiratory and wide pedal openings 

 communicating with the interpallial space, the two pairs of branchiae, 

 the mouth with the anterior and posterior lip and the four oral 

 palps, the foot, the extensive cloacal cavity with its subdivisions, and 

 the circular contractile cloacal orifice opening on the dorsal surface. 

 He next gives an account of the form and arrangement of the ali- 

 mentary canal, and its relations to the liver and large ovary ; and 

 describes a large viscus situated in the space between the ovary, the 

 adductor muscle, the base of the foot and the pericardium, divided 

 into a central and two lateral portions, and secreting a dark brown 

 liquid loaded with fatty matter. This body he thinks may be con- 

 nected with the secretion of the byssus, but, at the same time, 

 remarks that it may be homologous with the organ of Bojanus. 

 Lastly, the anatomy of the heart and great arteries is given, and is 

 in substance as follows. 



On cutting through the floor of the cloaca, the pericardium is laid 

 open, and in it is seen the large, rather square-shaped ventricle, with 

 a capacious but thin-walled auricle opening into it on either side, 

 through an orifice guarded by semilunar valves. From the thick- 

 walled ventricle, a short tube conducts into a conical dilatation or 

 bulbus arteriosus^ with muscular walls, having its base included 

 in the pericardium, and giving rise near its narrow end to the 

 anterior and posterior paUial arteries ; whilst a visceral artery 

 passes from the ventricle to the ovary and adjacent parts. As in 

 other bivalves, the intestine, before its termination, passes through 

 the heart: in coming through the pericardium, surrounded by 

 that membrane, it forms a short round pedicle which joins the fore 

 part of the ventricle ; it is then continued through the ventricle and 

 bulbus arteriosus, and finally opens into the cloaca. The blood 

 from the ventricle flows between the outer surface of the intestine 

 and the inside of the sanguiferous channel; and **that part of 

 the intestine which traverses the bulbus arteriosus is closely sur- 

 rounded with elongated membranous valvulee, which arise from the 

 anterior part of the chamber where the gut enters, and are fixed by 



