84 Prof. A. Mousson on the Molluscan Fauna of the Canaries. 



age, coustiiction of the perforation almost to its complete dis- 

 appearance, absence of yellow colouring, prevalence, on the con- 

 trary, of grey cloudy colours with fine dark lines. It appears 

 to live on the arid shores of both islands, and departs little or 

 nothing from the typical examples from the Alboran Islands, 

 except in the still more closed perforation. 



c. Var. geminata, MSS. This is distinguished as a very well- 

 marked variety, if not as a separate species, from the typical pi- 

 sana, by the somewhat depressed form, especially of the last 

 volution ; by the still sharper tine transverse striation crossed 

 by spiral grooves ; by the disappearance of all pohsh ; by the 

 want of perforation — often, indeed, of any indication of the same, 

 and that from its earliest stage ; lastly, by the abnormal character 

 of the colouring, which reminds one more of Alborunensis. On 

 the greyish and brownish-white ground are traced zones of fine, 

 entire or slightly interrupted, dark, spiral lines, radiating on the 

 spire, longitudinal at the circumference, which often form an 

 extremely elegant pattern, and remind one of the allied H. ustu- 

 lata, Lowe, of the Salvages Islands. More ])Oorly coloured 

 individuals have brownish-yellow clearly defined zones, with 

 distant rows of spots. In about forty examples from both 

 islands, eight were quite uncoloured. 



It is interesting to see these remarkable aberrations appear 

 on the most easterly of the Canaries, nearest to the continent, 

 whilst TenerifFe, except the closed perforation, already exhibits 

 nearly the European habit, and even this aberration disappears 

 again in the still more remote Madeiran and Azorian groups. 



2. Helix impugnata, MSS. 



Testa obtecte perforata, couvexo-depressa, solidula, lineis rugosis 

 transversis et subtilioribus longitudinalibus reticulata, opaca, griseo- 

 albida, lineolis numerosis brunneis interruptis ornata ; spira obtusa, 

 subprominula ; anfractus A\-i), superne planiusculi, filo-carinati ; 

 ultimus serrulato-carinatus, vix desceudens, subtus convexus ; 

 apertura luuato-securiformis ; perist. rectum, intus tenuiter labia- 

 tum, margiue columellari cameo, perforationem semiclaudente. 



Diam. maj. 12, minor 10^, alt. 8 millim. 



Mr. Webb has regarded this species as H. planata, Chemn., 

 M. D^Orbigny as a mere variety oi pisana, Miill. (/. c. p. 58), — 

 both, as I think, improperly. From planata, which, according 

 to PfeifFer (Mon. iii. 137), is a native of Africa, as well as fi-om 

 its ally, erythrostoma, Phil. (/. c. iii. 137), which comes from 

 Morocco, it is distinguished by the more elevated spire ; by 

 having one volution less ; by the keel being prominent like a fine 

 thread on all the volutions ; by the absence of all polish in con- 

 sequence of the fine sharp longitudinal, and wrinkly cross- 



