CARBONIFEROUS AGE. 39 



accordance with the estahhshed rules of nomenclature, for these shells, because 

 the type of the genus Leptodomus, as originally founded by Prof. McCoy (i. fragi- 

 lis, Carb. Foss. Ireland, 1844, 66), apparently belongs to an entirely different 

 group. On turning to Prof. McCoy's figure of this species (lb. pi. x, fig. 11), it 

 will be seen to be a short, high, ventricose shell, with gibbous distinctly incurved 

 beaks, and a nearly smooth, or merely striated surface, and rather well marked 

 muscular impressions. Indeed we are led by Prof. McCoy's figure and description 

 to think this shell not genericaUy distinct from some of the forms included by Prof 

 Koninck in his genus Cardiomorpha, though it may be a ScTiizodus, King. 



On the other hand, we think the shells under consideration, are not generi- 

 caUy distinct from Sedgtoiclda, McCoy, as originally proposed by him in his Synop. 

 Carb. Foss. 1844, p. 61, and typified by his *S'. attenuata (lb. p. 62). It may be, 

 however, that Prof. McCoy dropped the name Sedgivickia, because it had been used 

 several times in Botany. StiU we cannot regard this as a sufficient reason for 

 setting the name aside, for there are numerous instances where the same name is 

 retained for genera in Botany and Zoology. In addition to this, the particular 

 genus for which Botanists now retain the name Sedgwickia, was published by 

 Griffith, since the publication of Prof. McCoy's genus. Even if we admit, how- 

 ever, the propriety of abandoning the name Sedgwiclda, these shells cannot be 

 properly referred to Leptodomus, we should think, until it can be demonstrated, or 

 at least rendered probable, that they are congeneric with the type of that genus — 

 L. fragilis, McCoy. 



It is worthy of remark, also, that these shells resemble the typical AUorismas in 

 so many points that we have some doubts whether they should be separated more 

 than as a sub-genus. They are also rather closely allied to Myacites^ as affirmed by 

 Munster. From the typical species of the former genus, they differ in being 

 shorter and usually more gibbous shells, with more prominent beaks and umbonal 

 slopes. They also differ in having the postero-dorsal region more compressed, and 

 the cardinal margin more concave in outline behind the beaks. These peculiarities 

 give these shells a Lyonsia-Vike aspect apparently never seen in the true AUo- 

 rismas. In their less elongated form, and more prominent beaks, they approach 

 nearer some species of Myacites, but differ in the other characters mentioned. 



From the genus Sanguinolites, as originally defined, and typified by Sanguino- 

 laria? angustata of Phillips (McCoy, Carb, Foss. Ireland, 1844, 47 and 48), our 

 shells differ in being proportionally much shorter, more gibbous, less depressed, 

 and not near so straight and parallel on their dorsal and ventral margins. Until 

 something, however, can be determined in regard to the hinge or muscular and 

 pallial impressions of Sanguinolites angustatus, the type of that genus, we can form 

 no satisfactory conclusions in regard to its limits. It is true. Prof McCoy, in 

 re-describing this genus, in his- Brit. Pal. Foss. 1852, describes the muscular and 

 pallial impressions; but it is manifest these characters were taken from his S. 

 iridinoides, and other forms, that may or may not be congeneric with the species 

 angustatus. Should the S. iridinoides, however, really be congeneric with that 

 species, which is not improbable, it would rather confirm the conclusion that the 

 short gibbous shells imder consideration are genericaUy distinct, than the contrary. 



