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Conchoecia caudata, G. W. MÜLLER, 1906 a, p. 65; pi. XI. fig. 24 and pi. XII,
figs. 1—9.
„ dasyophthalma, ., ,, „ 1906 a, p. 66; pi. XI. figs. 20—23 and 26—30.
Is this group a natural one? A criticism oj this
As I was only able to investigate closely one of the above-mentioned species it is
exceed-ingly difficult for me to decide this question on account of the ineompleteness in the
descriptions of these forms. It seems to me, however, fairly certain that it must be answered in
the negative.
Both G. M. MÜLLER’s characterization of this group and C. Clals’s diagnosis of the
genus Paraconchoecia are exceedinglv incomplete and leave the reader anything but convinced
as to the justification of including the species in question in one group. G. W. Müller himself
states (1906 a, p. 52) that it is not possible to define precisely and characterize this group.
In order still further to explain this faet I shall give here a eritieal exposition of the characters
put forward by these writers.
Shell: — According to C. Claus this is „sehr zart und stark comprimiert, meist mit
einem Stachelfortsatz am Hinterende der rechten Klappe“. G. W. MÜLLER onlv adopts the
last of these charactere; according to the latter writer the shell is characterized, in addition,
by the tact that the unsymmetrical glands emerge for the most part ,,at the usual place“ and
by the absence of latéral groups of glands.
Witli regard to these charactere the following facts may be stated: The species of this
group that 1 investigated, namely C. oblonga, is not characterized by a more thin-walled shell
than many other species belonging to other groups of this genus. — The shells of species in this
group are not, or at least not essentially, narrower than in most other species of this genus. —
These two charactere were, as has been pointed out above, not included by G. W. MÜLLER. —
The posterior dorsal corner of the right valve is armed with a more or less well developed spine
not only in a rather large number (nineteen) of species belonging to several other groups of this
genus but also in representatives of two of the three other genera of this family, namely
Archi-conchoecia and Euconchoecia. In addition, an armature of this kind is, as both C. CLAUS and
G. W. MÜLLER have pointed out, not characteristic of all the species in the group under
considération here ; both C. inermis and C. dorsotuberculata have no spines at all either on the left or the right
valve. It is also to be noted that we are here concerned with a character that sometimes varies
even within the species, a faet that G. W. MÜLLER himself has observed; cf. this writer’s work
19(J6 a, p. 53. — The faet that the unsymmetrical glands have their exits ,,an der gewöhnlichen
Stelle“ is, of course, a character of little value. This character, which is found in most species
of the genus Conchoecia, is presumably an original one in this genus, as is shown with a fairly
great degree of certainty by the faet that these glands also have this position in the genus
Halo-cypris. Moreover these glands have, as G. W. MÜLLER himself has pointed out, been rather
considerablv displaced in not less than four species of this group, namely C. aequiseta, C. hirsuta,
C. dorsotuberculata and C. mamillata. — The absence of lateral groups of glands in these species
is certainly also primitive. Such groups of glands are only found in the genus Conchoecia;
in all other genera of this sub-family they are always absent. In the genus Conchoecia there are
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