438 



(I. e. 1895), the species described byLeidy and Silliman were so poorly 

 characterized, that the common sense rules of nomenclature do not 

 allow them to be maintained. Despite the poorness of Silliman's 

 diagnosis, from which it is impossible to learn whether the mouth- 

 opening is confluent with the rhynchodaeum, whether it is dioecish, 

 whether the nephridia reach to the end of the body, some recent 

 authors still hold that the New York species is a typical Tetrastemma ; 

 but a glance at Silliman's fig. 19 shows that the proboscis of his T. 

 aquarium dulcium is barely two-thirds as long as the animal , whereas 

 in the true Tetrastemma it is always at least as long as the animal. It 

 is not improbable that the '"'•Tetrastemma^^ aquarium dulcium may be 

 closely allied to the form which I have described here ; but a re-exa- 

 mination of Silliman's species must be made before this question 

 can be settled. The good effects of adhering to the law of priority in 

 nomenclature become nullified, when one endeavours to retain the 

 names which have been accompanied by imperfect descriptions; a 

 diagnosis is only then valid, or should only be, Avhen a species may be 

 recognized by its aid. 



In a communication from Dr. W. R. Coe, of New Haven, Conn., 

 I learn that this investigator has found a freshwater Nemertean in a 

 small pond near that town. 



5. Einige neue Hydrachniden-Formen. 



(Vorläufige Mittheilung.) 

 Von R. Pi ers ig. 



eingeg. 9. September 1896. 



Während meines Aufenthaltes in Ziegenrück (Thüringen) gelang 

 es mir neben Torrenticola anomala (Koch) Piersig (= Tiphys ano- 

 malus C. L. Koch) und dem Männchen von Aturus scaher Kramer 

 (nicht identisch mit Aturus scaher (^ Koenike , dessen aus Amerika 

 stammende Form ich mit dem Namen Aturus mirabilis Piersig belegte), 

 noch einige andere Wassermilben aufzufinden , die meines Wissens 

 noch nicht beschrieben Avorden sind. 



1. Sperchon clupeifer n. sp. 

 Größe 0,65 mm; Körperumriß fast kreisrund mit breitem Stirn- 

 rande; Oberhaut anscheinend netzartig gefeldert; jedes Feldchen von 

 18 — 25 feinen Chitinspitzchen eingefaßt; die Rückenfläche zum 

 größten Theile von einem rundlichen, großporigen Panzer bedeckt 

 (deshalb clupeifer), der ohne scharfe Umgrenzung in die weiche Kör- 

 perdecke übergeht; Grundfarbe des Körpers grünlichgelb bis bräun- 



