490 Dr. H. Woodward — On a New British Homalonotus. 



This section of Homalonoti is interesting on account of its wide 

 distribution, as may be seen by tlie following list : — 



1. Somalonotus Serschelli, Miirch., Devonian, South Africa. 



2. ,, armatus, Biu-m. ,, Eifel, Rhenish Prussia. 



3. ,, elongatus, Salter, ,, South Devon. 



4. ,, Fradoanus, De Vern. ,, Spain. 



The species described by Mr. Salter from the Lower Devonian, 

 Meadfoot Sands, S. Devon, as Homalonotus elongatus, is founded 

 upon a tail only, remarkable even in this elongated genus for its 

 lengthened shape. A careful study of JI. elongatus, Salter (given 

 on plate x. figs. 1 and 2, of Mr. Salter's Monograph, Pal. Soc. 1865, 

 part ii., British Trilobites, p. 122), leads me to conclude that Mr. 

 Champernowne's fossil cannot have belonged to this species. For 

 in all the Homalonoti, the thoracic somites jjass by an almost 

 insensible gradation into the tail-portion, with little or no change 

 in the style of ornamentation between the free and moveable ribs 

 of the thorax and the consolidated caudal series. The unique 

 specimen of M. elongatus in Mr. Townshend Hall's Collection is 

 very strongly trilobed, and appears to have had four pairs of spines 

 along its median axis, and two pairs upon the lateral portions. Mr. 

 Champernowne's specimen has little or no signs of trilobation, 

 being in this respect very like in form to the Homalonotus Herschelli 

 from the Cape, and M. delphinocephalus from Dudley. 



Although but a cast, from which all trace of the actual shell has 

 disappeared, the pseudomorph shows that this species had thirteen 

 free and moveable thoracic ribs with broadly expanded pleurae 

 each armed with a pair of spines placed about one inch apart and 

 forming two parallel rows. The glabella is oblong and has three 

 pairs of spines placed on the lateral portion and three along the 

 median line, of which the most anterior appears to have been 

 double. There is no evidence of any cheek-spines. 



The ej'^es apjoear to be situated nearer to the genal border than in 

 H. armatus, and the rostrum is rather more prominently developed. 

 If we assume the tail-portion when perfect to have been two inches 

 (which is fully within tlie relative proportions — ^judging from many 

 other species), this would give the Torquay specimen a length of 

 8 inches and a breadth measured along the curve of the thorax at 

 its widest part of 3|- inches. 



The Eifel species (H. armatus) is relatively broader and shorter, 

 measuring 6 inches in length by 3 inches across the widest part of 

 the thorax. 



The fossil displays almost better than any other specimen I have 

 seen the beautiful cardinal or hinge-like joints by which the segments 

 of the thorax are articulated with one another ; precisely the same 

 in construction as the hinges in the jointed somites of the tail of a 

 living lobster. (See Plate XIII. B. side-view.) 



After careful comparison with the other species, I am led to con- 

 clude, fi'om the position of the eyes, the spines on the head, the 

 proportions of the thoracic somites, and the relative size of the fossil 

 as compared with its two nearest allied forms, H. armatus and H. 



