OFCONCnOLOGY. -! Jj 



NOTE ON THE BUCCAL PLATE (JAWJ IN CERTAIN 

 GENERA OF THE FAMILY CYGLOSTOMACEA. 



BY THOMAS BLAND. 



Gray and PfeiiTer arranged the Cjclostomacea in various 

 subfamilies, mainly distinguished by diii'erences in the charac- 

 ters of the operculum. Troschel {(jehiss Der Schnecken, part 1, 

 1856,) with especial reference to the form and arrangement 

 of the teeth on the lingual membrane, and considerations as 

 to the buccal plate, divides the Cyclostomacea examined by 

 him into three families, embracing the following genera : 



PoMATiACEA. — Grcn. Pomutias. 



Cyclotaoea. — Gen. Gyclolus, Graspedopoma^ CycJophorus 

 and Rherjostoma. 



CrcLOSTOMACEA. — Gen. Cyclostomus, Leonia, Ghondroporaa, 

 Twlora, Ghoanopoma and Gist /da. 



It is remarkable, and I believe not generally understood, 

 that the buccal plate is found in Pomatiacea and Gyclotace.a, 

 but not in Gyclostomacea. My attention was lately directed 

 to this subject by my friend, Mr. Eobert Swift, of the Island 

 of St. Thomas, W. I., who sent to me specimens of the bnccal 

 plate, taken and prepared for microscopic examination by 

 himself, from the animals of Gyclotus stramineus- sand M> galo- 

 mastorna cylindrace.um. Troschel describes (p. 65) the jaw 

 {ki.efer) of Pomaticis patuhis as consisting of two thin laminae, 

 having 20 parallel rows of rhombodial scales of yellowish 

 color, directed obliquely from the upper towards the anterior 

 margin, to which II: of the rows extend, causing it to be 

 irregularly serrated. Towards the posterior margin the scales 

 are less colored, more transparent, and disappear at some dis- 

 tance from the margin of the membrane, on which they seem 

 to be inserted. In the single rows, the scales are always 

 c[uadrate, or rather rhombical, becoming shorter, but more 

 elevated towards the anterior mag-in. 



O 



The structure of the jaw in Gyclotacea, is said by Troschel 

 (p. 66) to be entirely similar to that in Pomatiacea, indicating, 

 as he remarks, a close relationship. He gives a figure (Taf. 

 iv., fig. 3,) of the jaws of Graspedopoma lucidum, Lowe, ob- 

 serving that it agrees completely in organization with that of 

 Pomatias patulus. 



The jaw of Gyclolus straminevs, as shown by our fio-ure 1. 

 plate 5, accords with Troschel's description. 



Troschel (1. c. p. 68) states that he had examined species of 



