80 Dr. J. D. Macdonald on the Anatomy of Diplommatina. 



misunderstanding should arise as to the apparent situation of 

 the eyes in fig. 2, it should be stated that the object was 

 viewed by transmitted light — a circumstance that might ac- 

 count for the original mistake, had the animal been so ob- 

 served. In regard to the supposed relationship of Diplomma- 

 tina to Acicula, I can only say, not having been able to exa- 

 mine any of the typical Aciculce, that, if they are indeed allies 

 of Truncatella, they have nothing to do with Diplommatina. 



The next important contribution to the anatomy oi Diplom- 

 matina is to be found in a short paper by Mr. R. J. L. Guppy 

 " On the Occm'rence of Diplommatina Huttoni in Trinidad " 

 (Ann. & Mag. Nat. Hist. 1867, vol. xx. p. 96), the more per- 

 tinent part of which runs thus : — " The lingual dentition, 

 being very minute, is somewhat difficult of preparation ; but I 

 have been able to make out its characters, which are as fol- 

 lows : — The dental band is of moderate length ; the teeth are 

 3.1.3, the median is broad, its edge narrowly reflexed and 

 five-toothed, its base narrow, almost pointed. The first and 

 second laterals are subclavate, their edges reflexed and three- 

 toothed. The third lateral is somewhat hamate and obscurely 

 tricuspid. The mandible is broad and flat, covered with very 

 distinct, separate, lozenge-shaped plates. All this tends to in- 

 duce one to retain this genus in the Cyclophorid^, to which 

 these characters attach it more closely than to the Cyclosto- 

 midse." In these remarks we find a recognition of the dis- 

 tinctness of the two families named, and of what is unques- 

 tionably the true position of Diplommatina. The amber- 

 tinted labial plates, composed of obliquely rhombic cells, first, 

 I believe, noticed by myself in Pupina and Diplommatina^ ^ are 

 quite characteristic of the Cyclophoridse ; for although very 

 similar organs are present in Natica and Triton and their 

 allies amongst marine Proboscidifera, the labial plates of Cy- 

 clostoma, Hydrocena, and Assiminea are very different. I 

 have now only to remark that the dentition of Pupina is so 

 identical with that of a species of Cyclophorus (fig. 10) occur- 

 ring at the Isle of Pines, that I did not think it necessary to 

 furnish a drawing of it. On the other hand, the dentition of 

 Diplommatina makes a nearer approach to that of Cyclophorus 

 aquilum figured byMr.WoodAvardf, the central dental plates in 

 particular being expanded in front to support a greater number 

 of teeth. The recognition of the two types here indicated will 

 be of importance in the distribution of other genera referable 

 to the Cyclophoridse. 



* In a paper read before the Royal Society, Feh. 26, 1857, " On the 

 Natural Affinities and Classification of Gasteropoda." 

 t Manual of Mollusca, p. 175. 



