Dr Fleming on the British Testaceous Annelides. 247 
Genus HETER0D]SCA. — Shell with the spires sinistral. The 
reverse character in the following species is uniform, and thus, 
independent of other circumstances, forbids us to regard them 
as accidental varieties of any of the species of the former genus 
Spirorbis. 
a. Shell with longitudinal ridges. 
Species 1. H. heterostropha — Shell triangular, with three ridges. Serpula 
het. Mont. Test. Brit. p. 503 — Spirorbis het. Flem. Edin. Ency. vii. p. 68. 
tab. ccv. f. 1. On stones and shells, common. 
The shell is white, opaque, with three lateral whorls, the last and part of 
the second only apparent. The base spreads a little. The middle ridge 
is prominent, the lateral grooves are wrinkled, and the lateral ridges are 
indistinct. The inner ridge forms in part the central cavity. 
2. H.*minuta Shell rounded, with two grooves. Serpula minuta, Mont. 
Test. Brit. 505 Spirorbis minutus, Flem. Edin. Fncy. vii. p. 68. tab. ccv. f. 2. 
On rocks, stones, but especially the Corallina officinalis, common. 
The grooves, on the back, form that part into three obsolete ridges. The 
central cavity exposes more of the second whorl than in the preceding 
species. According to Montagu, the inhabitant has ciliated branchiae, 
and a clavate lid, varying from brown to green. This species adheres 
to substances exposed directly to the motion of the waves, while the he- 
terostropha occupies a more sheltered station, attached to the under side 
of stones. 
3. H. conica Shell triangular, with a single groove. Flem. Edin. Ency. 
vii. tab. ccv. f. 3. On shells, Zetland. Coast of Appin, Captain Carmichael. 
When young, the upper part of the whorl has a distinct groove, with a low 
acute ridge on each side, and a very small central cavity. In this state, 
the whorls are two in number, the outer one lateral, with a spreading 
base. The third whorl, in its growth, not only embraces the others la- 
terally, but ascends, and forms the outline of the shell into a truncated 
cone, with the mouth at the top, sublateral. The groove and central 
cavity are in this state less distinct, the latter generally obliterated. It 
is a strong shell, and remarkable for being hyaline, like Vermilia serru- 
lata. It is seldom found but on stones and shells brought from deep 
water. 
b. Shell destitute (^longitudinal ridges. 
4. H. lucida — Shell smooth, glossy, subcylindrical, with a blunt apex. 
Serpula quatuor anfractibus umbilicata apertura rotunda, and S. apertura ro- 
tunda anfractibus duobus umbilicata. Walk. Test. Min. p. 4. tab. 1. f. 13, 14. 
Serpula reflexa, Adams, Linn. Trans, v. p. 4. tab. tab. 1. fig. 31, 32 — S. sinis- 
trorsa, Mont. Test. Brit. p. 504 — Serp. lucida, ib. p. 506. — Spirorbis lucidus, 
Flem. Edin. Ency. vii. p. 69. tab. ccv. f. 4. On crustaceous animals and co- 
rallines, common. 
The shell is nearly cylindrical, translucent and glossy. When growing oh 
an even surface, it forms two or three lateral whorls, with a small cen- 
tral cavity. When seated on corallines, its growth is very irregular. 
The whorls, in some, are placed contiguous, one above the other, with 
the aperture ascending, while, in others, the shell is simply twisted, 
round, and unconnected. So variable, indeed, is this species, that scarce- 
ly two specimens can be found alike, a circumstance which has ^iven rise 
to the preceding synonymes. According to Montagu, the animal (his 
lucida) is red, Avith pale plumose branchise, and two brown spots on the 
head. 
